Japanese Iron Coin with Round Hole

In some books this coin mentioned as Japanese, issued in 1875. But background is uncleared for me.

Your coin is a regional issue from Hakodate in Japan, made in 1856. The legend reads (in Japanese) Hakodate Tsuho (current coin of Hakodate). It is listed in my 1987 edition of the Catalog of Japanese Coins and Banknotes as worth between 200 and 1000 yen in average condition.

This is indeed a provincial coin from Oshima province on the island Hakkaido.
On the reverse side on top of the hole is the character AN. This is for the designation of the AN SEI reign period (1854-59) of the KOMEI emperor.
The piece is mentioned also to exist with an octagonal instead of a round central hole.