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A History of Coins
1-6 Keicho Koban: Establishment of the Unified Currency System
Keicho Oban (Weight: 165.4grams/  Fineness: 68percent gold)	Keicho Koban (Weight: 17.9grams/  Fineness: 84percent gold)	Keicho Ichibu-kin (Weight: 4.5grams/  Fineness: 84percent gold)
	Keicho Cho-gin ( Fineness: 80percent silver)	Keicho Mameita-gin ( Fineness: 80percent silver)
Gold and Silver Coins of the Keicho Era(1596-1615)       　In 1601, Tokugawa Ieyasu minted five varieties of gold and silver coins, for mutual exchange at market rates.

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Immediately after defeating his enemies at Sekigahara (in what is now Gifu Prefecture), thereby winning political control of Japan, Tokugawa Ieyasu embarked on the unification of the currency system, to secure economic control over the nation. In 1601, he ordered the mintage of Keicho gold and silver coins such as the Keicho Koban and laid the foundation for the Edo Period's currency system, which lasted for about 270 years.       Gold coins were minted by tale in units of ryo (approximately 15 grams), based on the scaling system followed by Koshu gold coins minted under Lord Takeda of Kai province (now Yamanashi Prefecture). Keicho gold coins consisted of the oban (10 ryo), which served primarily as a reward or for ceremonial purposes, and the koban (one ryo) and ichibu-kin (1/4 ryo), which were issued as a means of exchange in daily life. The oban was exchanged according to gold content rather than face value, and was valued at approximately 7.5 ryo. The cho-gin (a form of slug) and mameita-gin (a form of bean) silver coins, on the other hand, were minted as money by weight, since silver coins were commonly used as a means of exchange according to weight in economically developed western Japan. Concurrently, the Tokugawa Shogunate placed major gold, silver, and copper mines throughout the country under its direct control and collected gold and silver in circulation via its Kinza (gold mint) and Ginza (silver mint), to secure materials for mintage.       Tokugawa Ieyasu's unified currency system based on Keicho gold and silver coins was thus put into effect by consolidating and integrating the gold and silver coins already in circulation. At the same time, the unification of small-denomination coins lagged, with mintage of the one-mon copper coin called Kan'ei Tsuho beginning only in 1636 (the Kan'ei Era lasted from 1624 to 1644). In 1608, the official conversion rate for gold, silver, and copper coins was fixed at one ryo of gold to 50 momme of silver to four kammon of copper, but in reality the rates fluctuated daily, reflecting market conditions. Moreover, gold and silver coins circulated differently in various parts of the country. As is evident from the saying "Gold in the east, silver in the west," gold coins were used to settle the majority of transactions for goods in the east, as opposed to silver coins in the west.       The currency system of the Edo Period is often described as a unified currency system, Since its basic currencies consisted of three types of coins-namely, gold, silver, and copper. Yet it was not until the Kambun Era (1661-73) that the three types of coins became widely used throughout the country as a means of payment.

Naoto Yamaoka: Research Division 3, Institute for Monetary and Economic Studies, Bank of Japan Monetary and Economic Studies 15(1), Bank of Japan, 1997

References Bank of Japan, Economic Research Department, ed. Japanese Coins, Vol. 1, Toyo Keizai Shimposha, 1972 (in Japanese) Mikami, Ryuzo, The Story of Money in the Edo Period, Toyo Keizai Shimposha, 1996 (in Japanese). Suzuki, Kozo, Economic System of the Edo Period , Nihon Keizai Shimbunsha, 1995 (in Japanese).