A cap of a high-pressure gas tank includes a first member and a second member. The first member is located on the inner side of a liner. The second member is located on the outer side of the liner and is connected to the first member. A rotation restricting structure includes a first rotation restricting portion and a second rotation restricting portion. The first rotation restricting portion is provided on an inner surface of the liner. The second rotation restricting portion is provided on the first member so as to be fitted into the first rotation restricting portion.