Wadokaichin is the oldest official Japanese coinage, having been minted starting on 29 August 708 on the order of Empress Genmei. These coins were round with a square hole at the center of each coin to make it easier to hold the coins on a string. They remained in circulation until 958 CE. These were the first of a series of coins collectively called junizeni or kocho junisen.

Wadokaichin is the four characters printed on the coin. Its name is derived from the era name Wado (“Japanese copper”) and could also alternately mean “happiness” and “Kaichin,” which is thought to be related to “Currency.”

This coinage was inspired by the Chinese Tang dynasty coinage named Kaigen Tsuho, first minted in Chang'an in 621 CE. The Wadokaichin had the same specifications as the Chinese coin, with a diameter of 2.4 cm and a weight of 3.75 g.

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