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A History of Coins
1-7 Kan'ei Tsuho and Tempo Tsuho
Kan'ei Tsuho (Copper, one mon) (1636) Diameter: approx. 24mm Weight: approx. 3.75g	Kan'ei Tsuho (Copper, one mon) (1668) Diameter: approx. 24mm Weight: approx. 3.6g This coin was called bunsen, because of the Japanese character bun on its reverse side.	Kan'ei Tsuho (Brass, four mon) (1768) Diameter: approx. 27mm Weight: approx. 4.9g A simpler coin with fewer waves on the reverse side was minted from 1769.
Kan'ei Tsuho This coin was minted throughout the country for 300 years--from the beginning of the Edo Period until the start of the Meiji Period--as the official coin of the Tokugawa Shogunate.
Tempo Tsuho (100 mon) (1835) Length: approx. 49mm; Width: approx. 32mm Weight: approx. 20.6g
Tempo Tsuho This coin was minted in the later years of the Edo Period with a face value of 100 mon. Illicit minting of the coin occurred throughout the country due to the significant difference between face value and material value, as the coin was worth only five pieces of one-mon copper coins.

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Chinese coins that flowed into Japan in large quantities played an important role in economic development in terms of payment settlement, because they were used in Japan as a domestic currency. From the latter half of the 15th century, numerous types of coins began to circulate in Japan, as concerns over the deteriorating quality of the imported Chinese coins (due to chips and cracks) led to an inflow of copper coins from Korea, the Ryukyus, and Annan as well as privately minted coins. As a result, establishing a unified currency system was not an easy task. It took the Tokugawa Shogunate 35 years after it began minting gold and silver coins to replace imported and privately minted coins with the Kan'ei Tsuho.       Aiming to eliminate the practice of erizeni (selection of coins), the shogunate set an exchange ratio of l:4 between the eirakusen and bitasen, which played an important role as a base calculation coin. Coins other than the eirakusen were circulated at one-fourth the eirakusen's value. Despite these measures, the practice of erizeni did not cease. Consequently, in 1608 the shogunate banned the use of the eirakusen as a base currency, standardized the exchange value of all coins based on that of the bitasen, and enforced the official exchange ratio of the Edo Period currency system of one gold-coin ryo to 50 silver-coin momme to four base-metal-coin kammon. However, the practice of erizeni continued.       In 1636, the shogunate minted and issued the Kan'ei Tsuho and at the same time tried to collect all old imported and privately minted coins. Owing to the increasing number of zeniza (copper mints), the Kan'ei Tsuho was minted in large quantities, circulating throughout the nation during the Kambun Era (1661-73). In 1670, the use of coins other than the Kan'ei Tsuho was prohibited. The old coins collected in exchange for the Kan'ei Tsuho are believed to have been exported to neighboring East Asian countries either in their original form or recoined into the hokusosen.       The size and shape of the Kan'ei Tsuho varied, since the coins were minted by local merchants under contract. Moreover, after the start of the 18th century, the one-mon and four-mon copper coins were minted using steel and brass due to the shortage of copper. In 1835, as the Tokugawa Shogunate drew to a close, a large copper coin called the Tempo Tsuho-with a face value of 100 mon-was also minted.

Mari Ohnuki: Research Division 3, Institute for Monetary and Economic Studies, Bank of Japan Monetary and Economic Studies 15(2), Bank of Japan, 1997

References Bank of Japan, Economic Research Department, ed. Zuroku Nihon no Kahei (Japanese Coins), Vols. 2 (1972) and 4 (1973), Toyo Keizai Shimposha (in Japanese). Mikami, Rryuzo, Edo no Kahei Monogatari (The Story of Money in the Edo Period), Toyo Keizai Shimposha, 1996 (in Japanese). Nakajima, Keiichi, “Nishi to Higashi no Eirakusen (Eirakusen of the East and West),”　in Susumu Ishii, ed. Chusei no Mura to Ryutsu (Villages and Circulation of the Medieval Period), Yoshikawa Kobunkan, 1992 (in Japanese).