To mount a chain case for a bicycle easily to the bicycle.

This chain case for a bicycle is provided with a chain case body 11 having a gear covering part 26 and a chain covering part 27, and a fitting member 12 for fixing the chain case body 11 to the bicycle side. A fixing boss 37 provided at the peripheral part of the gear covering part 26 is insert- fitted into one end part of the fitting member 12 so as to fix a part of the peripheral part of the gear covering part 26 to one end part of the fitting member 12, and the other end part of the fitting member 12 is inserted between a lateral pair of holding pieces 39, 40, provided at the peripheral part of the gear covering part 26, so as to regulate the lateral movement of the other end part of the peripheral part of the gear covering part 26 in relation to the other end part of the fitting member 12.