FUEL TANK

A fuel tank has a built-in component (6) with a head portion (6d), a neck portion (6c), and a shoulder portion (6b), and has the built-in component (6) anchored to a tank body with a parison (SA) wrapped around the neck portion (6c) during molding. The fuel tank includes a deformation prevention structure configured to prevent a wrapping parison portion (W) wrapped around the neck portion (6c) from being deformed due to pressure acting on the tank body. The deformation prevention structure is configured to include one of a stepped portion (6h) provided in the shoulder portion (6b), a convex portion, and a recess.