To make it hard to expose a fixing bolt and a fixing nut to the outside when fixing a fixed object to an object by the fixing bolt and the fixing nut.

A cavity is formed between the surface of a license plate 1 and a collar part 11 of a collar member 10 mounted to the lower end of a head 2a of the fixing bolt 2 for fixing the license plate 1. A crowning member 20 is put on the head 2a of the fixing bolt 2 and the collar member 10. The lower end of a sidewall part 22 of the crowning member 20 is formed with a collar member locking claw 23 inserted between the collar part 11 and the surface of the license plate 1. A circular projecting part is formed at the lower end of an internal wall surface of a peripheral wall member 30 of hollow cylinder shape. The circular projecting part presses the sidewall part 22 of the crowning member 20, and peripheral wall member locking claws 24, 25 are engaged with the circular projecting part.