This coin was minted by the Tokugawa Shogunate during the Edo Period (1603-1868). They were issued throughout three different Japanese eras: the Meiwa Era (1769-1788), the Bunsei Era (1821-1825) and the Ansei Era (1857-1859). The obverse of the coin displays the Japanese characters Kan Ei Tsu Ho and the reverse features 11 waves. Each coin has a diameter of about 28mm. 

Unlike our modern coins, which are struck using dies, these Japanese coins were produced via sand casting. After the coins were cast, they would then be filed down. As a result of this process, the raised areas of the coin are smooth whereas the lower areas still show the texture of the sand that was used to cast the coin. On some coins, you can still see the original file marks. The coin you purchase may differ slightly from the examples in the photographs due to age, wear, casting irregularities and the different metal alloys used during the three different eras of production (Meiwa, Busei and Ansei Eras). 

This coin is a must have for anyone with an interest in Japanese culture and history. It was introduced to replace an earlier coin that has 21 waves on its reverse, minted from 1768 to 1769. I also have these rarer coins for sale on eBay.