Tank cap

A fuel cap (10) of the invention includes a spring stopper mechanism (70) to lock a first spring (68) included in a pressure regulating valve (50) of the fuel cap (10). A spring stopper mechanism (70) includes stopper support members (71) that are formed along an inner circumference of a valve chest formation-member (20b), and a spring support member (75) that is held by the stopper support members (71) and supports an upper end of the first spring (68). The spring support member (75) is pressed down in an axial direction of the fuel cap (10) against a pressing force of the spring (68). The spring support member (75) at the pressed-down position is rotated relative to the stopper support members (71) by a preset angle. The spring support member (75) is then pressed against the stopper support members (71) by the pressing force of the spring (68) and is fixed by mating lock elements (77). This arrangement of the invention facilitates assembly of a pressure regulating valve and ensures sufficiently high assembly strength.