Hi, that would be a really early netsuke. It looks like it is made of some kind of bone? Did you buy it from a specialized dealer? I am still learning in this field and will make no guesses about age & authenticity. There are some simple old everyday netsuke, but there were also made incredibly many souvenir pieces and fakes. To be sure, post your piece in the specialized forum, the people there will tell you for sure:
http://forums.netsuke.org/Mat