Keichō Koban (慶長小判) — The Symbol of the Early Modern Monetary System Built by Tokugawa Ieyasu

On the 15th day of the 9th month of Keichō 5 (1600), Tokugawa Ieyasu defeated the Western Army led by Ishida Mitsunari at the Battle of Sekigahara, effectively becoming the ruler of the realm. Yet what Ieyasu had in view was not merely military victory, but the establishment of a long-lasting system of control. During Japan's Sengoku period, various daimyo had each issued their own gold coins — the Kōshū-kin minted by Takeda Shingen, the domain currencies of the Later Hōjō clan, the Suruga Takeda-kin, and others. Fineness varied greatly by region, and even the Kōshū ichibu-kin (甲州一分金), which circulated in Shingen's territory, was routinely discounted when traded in the Kamigata region or the western provinces.

Ieyasu regarded this fragmentation of currency as a hindrance to the development of the commercial economy. Already in the Tenshō era (1573–1592), Toyotomi Hideyoshi had issued the Tenshō Ōban (天正大判), but this was closer to a gift coin for rewards and was not intended for market circulation. What Ieyasu envisioned was a koban as a "practical currency" circulating throughout the entire country.

It is said that at the end of Keichō 5, once the post-war settlement had settled down, Ieyasu made his final decision on monetary unification at Fushimi. On the technical side, he brought in the foremost authorities in goldsmithing of the day, including Hon'ami Kōtoku and Gotō Shōzaburō Mitsutsugi; on the political side, he simultaneously advanced policies to incorporate gold and silver mines into directly administered shogunal domains (tenryō). The Sado gold mine, the Izu gold mine, and the Kai gold mine were brought one after another under direct shogunal control, and with the supply of gold firmly in hand, the stage was set for the commencement of koban minting at the beginning of Keichō 6.

Monetary unification is a symbol of political unification — this political instinct, shared by Augustus of ancient Rome, Emperor Gaozu Li Yuan of the Tang dynasty, and the Hongwu Emperor of the Ming dynasty, was one that Ieyasu possessed as well. The birth of the Keichō Koban was another grand "national project," one that preceded the formal establishment of the Edo shogunate as a warrior government (1603).

An indispensable figure in any account of the Keichō Koban is Gotō Shōzaburō Mitsutsugi (後藤庄三郎光次). The Gotō family was originally a prestigious house of goldsmiths in Kyoto, with an honorable lineage of service to the Muromachi shogunate. Mitsutsugi, who had become the adopted son of the main Gotō line's Gotō Tokujo, was recognized for his talent and engaged by Ieyasu. In Keichō 6, Ieyasu granted Mitsutsugi the position of head of the gold mint and entrusted him with the entirety of koban minting and quality control.

The kakihan (花押) — a kind of personal seal or signature — that Mitsutsugi stamped has been regarded as the single most important clue for distinguishing genuine Keichō Koban from counterfeits, right up to the present day. The kakihan, which bears the characters「光次」prominently within a fan-shaped frame, was passed down hereditarily by successive heads of the Gotō family, and the fine details of its brushwork functioned as a "national authentication mark" that counterfeiters could not reproduce. Behind Ieyasu's granting of such authority to the Gotō family lay a strategy: rather than having the warrior class directly produce currency, he delegated the "authority of minting" to a trusted community of goldsmithing specialists, thereby securing societal confidence in the currency itself.

The gold mints were established at three locations — Edo (Nihonbashi Honshoku-chō, near the present-day site of the Bank of Japan's main branch), Kyoto (Ryōgae-chō), and Sunpu (later abolished) — with the Gotō family overseeing all of them. Mitsutsugi managed all aspects of gold fineness testing, weight inspection, and the stamping of official seals (gokuin), and strictly policed unauthorized minting. Punishments of the time were severe; counterfeiting could result in death by crucifixion (haritsuke).

Mitsutsugi's grave is at Aoyama Cemetery in Minato Ward, Tokyo, and has become one of the "sacred sites" visited by modern coin collectors. The Gotō family's control of the gold mint continued for a full 260 years, all the way to the Man'en Koban (万延小判) of 1860 at the end of the Edo period. The two characters「光次」engraved in the gokuin of the Keichō Koban were a symbol of the artisan's craft that underpinned the very authority of the Tokugawa shogunate.

In Keichō 6 (1601), the minting of the Keichō Koban finally commenced. On the obverse, the gokuin「壹两」(ichiriō, meaning one ryō) was prominently stamped, with the「光次」kakihan within its fan-shaped frame below it. The reverse was worked with fine vertical lines called gozame-me, a practical measure to prevent wear and shaving. The specifications — approximately 70 mm in length, approximately 38 mm in width, a weight of 17.97 g, and a gold fineness of 84.3% — became the "ideal form of currency" that the shogunate aimed for throughout the Edo period.

The number of coins minted is estimated at approximately 14,700,000, a staggering quantity relative to the scale of Japan's economy at the time. Because minting was carried out simultaneously at the three gold mints in Edo, Kyoto, and Sunpu, minor differences can be seen in the details of the gokuin depending on the place of production. Edo-minted pieces are particularly fine in workmanship; Kyoto-minted pieces display a magnificence that represents the pinnacle of traditional goldsmithing; and Sunpu-minted pieces are highly rare.

How did the Keichō Koban actually circulate in the marketplace? With the establishment of the "three-currency system" (sankа seido) — comprising the Keichō Ichibu-kin (慶長一分金, a gold coin worth one-quarter of a koban) issued at the same time, and the silver coins Keichō Chōgin and Mameitagin — a basic exchange rate was formed at roughly 1 ryō in gold = approximately 50 monme in silver = 4 kanmon in copper cash. However, the gold-silver exchange ratio fluctuated in the market, and during the Genroku era it sometimes exceeded 1 ryō in gold = 60 monme in silver.

A distinctive dual structure emerged: the Kamigata economic sphere centered on Osaka and Kyoto was "silver-based," while the Kantō economic sphere centered on Edo was "gold-based." This gave rise to a new profession, the money changer (ryōgaeshō). The origins of great merchant houses such as the Mitsui, Sumitomo, and Kōnoike families can be traced back to the money-changing business of this period. The Keichō Koban was not merely a coin; it was the "infrastructure" that gave birth to Japan's early modern commercial economy itself.

After the Keichō Koban had circulated for 94 years, the first recoinage was finally carried out in Genroku 8 (1695). The recoinage was led by荻原重秀 (Ogiwara Shigehicle), a comptroller of finances (kanjō-ginmiyaku) who wielded great influence as a close aide to the fifth shogun Tokugawa Tsunayoshi. At the time, the shogunate's finances had fallen into serious deficit, due to reconstruction costs from the great fires of Edo, expenses for the construction of temples and shrines (particularly temple construction carried out at the behest of Tsunayoshi's mother, Keishōin), and declining output from the Sado gold mine.

Ogiwara proposed a policy of recalling the Keichō Koban in circulation, minting new koban with a reduced gold content, and using the resulting margin (deme/出目) as shogunal revenue. The fineness of the Genroku Koban (元禄小判) plummeted to 56.4%, a drop of 27.9 percentage points compared to the Keichō Koban's 84.3%. The weight was kept at the same 17.81 g, but the actual gold value had diminished by more than 30%.

This recoinage naturally caused great confusion in the market. Arai Hakuseki (a Neo-Confucian scholar who would later oversee shogunal administration in the Shōtoku era) sharply criticized Ogiwara's recoinage, arguing that it had "brought the credibility of currency crashing down." Ogiwara, for his part, is said to have propounded a pioneering monetary theory — with some variation in the accounts — to the effect that "currency is determined by the state and is not determined by the quantity of metal" (a view that foreshadows later inconvertible paper currency).

As a result of the Genroku recoinage, Keichō Koban in circulation were rapidly recalled and melted down. The recoinaged Keichō Koban became the Genroku Koban (元禄小判), and the path never returned to the starting point of Edo-period monetary history, which continued with the Kyōhō Koban (1715) and the Genbun Koban (1736). The reason so few Keichō Koban survive today lies in this large-scale recall through recoinage.

The 94-year history of the Keichō Koban also marked a watershed in Japan's monetary thinking — a shift from the early Tokugawa ideal of "authority backed by fineness" to the post-Genroku model of "credit created by power." The Keichō Koban was the last currency in Japanese history that was truly "the nation's gold" in the purest sense of that term.