A high-pressure gas tank includes: a tank body section; a base attached to an opening of the tank body section; a valve attached to an opening of the base so as to open and close a gas supply-discharge port of the tank body section, a part of the valve being inserted in the base, and the valve having a contact surface that contacts a seat surface as a surface of an end of the base, the surface of the end of the base forming the opening of the base; and a seal member arranged between an outer peripheral surface of a portion of the valve that is inserted in the opening of the base and an inner peripheral surface of the base. A slit for forming a communication hole communicating between outside of the high-pressure gas tank and a space between the base and valve is provided.