To provide a crime preventive cap for generating a crime preventive sound by opening and closing the cap, when supplying an oil into a domestic petroleum fuel tank.

A V-shaped spring is attached not fixedly but holdingly at a cut groove, in an inner circumferential part of the groove of a cylindrical column, corresponding to two lower positions of ear portions 3 for fixing a tank and the cap, in a cap inside of the oil supply cap. A V-shaped groove is provided in a portion abutting to the spring, in an outer circumferential part of an oil supply port in a tank side.