A fuel cap (60) for openably and closably covering a fuel filler (16a) of a fuel tank (16) includes a breather passage 80 allowing communication between the inside and the outside of the fuel tank (16). The breather passage 80 is provided with a breather valve mechanism 120 and a resonator chamber 81 as a silencing mechanism. The breather mechanism 120 is a valve 91 having a spring (111) capable of retaining a pressure within the fuel tank (16) up to a predetermined pressure. The fuel cap of the invention can prevent squeaking that occurs in a breather valve and a passage in a fuel cap provided with the breather valve, reduce a load on the environment, and also reduce cost.
