To provide a helmet wearing indicator to be mounted on a helmet 8 by keeping hooks 4 attached to both ends of a belt 2 hooked on a lower rim 8a on both right and left sides of the helmet 8, wherein a kind of the hook 4 can support helmets 8 different in a substantial hooking thickness T of the lower rim 8a.

The hook 4 includes an outer area 9, a base 10, an inner standing area 11 and a swell 12 swelling upward on the upper surface of the base 10: for a helmet 8 with a small substantial hooking thickness T of the lower rim 8a, the lower rim 8a is inserted between the outer area 9 and a side of the swell 12 thereby causing the hook 4 to be engaged with the lower rim 8a. While, for a helmet 8 with a large substantial hooking thickness T, the lower rim 8a is inserted between the outer area 9 and the inner standing area 11 and also onto the swell 12, thereby causing the hook 4 to be engaged with the lower rim 8a.