FUEL TANK

A fuel tank includes a tank body and a built-in component (6), which has a head portion (6d), a neck portion (6c), and a shoulder portion (6b), the built-in component (6) being anchored to the tank body with a parison wrapped around the neck portion (6c) during molding of the tank body. The head portion (6d) and the neck portion (6c) are formed with at least one hollowed portion (6k), which is open to an end surface of the head portion (6d), and a cap member (6e) is provided to seal an opening of the at least one hollowed portion (6k).