Patent ID: 7823611

Claim:
A filler cap of a fuel tank comprising: a cap main body attached to a fuel inlet of the fuel tank, the cap further comprising: an air passage which is constituted at the cap main body and which allows the inside of the fuel tank to communicate with the outside; and a valve mechanism portion constituted at this air passage, the valve mechanism portion including a tube main body having a cylindrical portion and a reduced diameter portion formed externally and continuously from this cylindrical portion, a float stored in the tube main body with a space between the float and an inner surface of this tube main body, a piston positioned on a fuel tank side of this float and stored in the tube main body with a space between the piston and the inner surface of the tube main body, and a spherical member positioned on an outer side of the float and stored in the tube main body, wherein, in a case where the fuel enters the tube main body, the piston moves toward the outside, the float floats toward the outside and the spherical member is pressed onto the reduced diameter portion of the tube main body by the float to close the air passage.