To securely fix a base body to a device having a vehicle structure at the time of fitting by using a stopper mechanism so as to support a base body with a lock element, which is separated in the reverse direction to the inserting direction.

A mounting device H is fixed to a vehicle supporting structure at a final fitting position, and fixed to lock elements V1, V2, and supporting shoulder parts 27 of the lock elements V1, V2 are engaged with notch edges 21b, 21a of a notch 21 from rear thereof. A lock wedge body 4 is pushed between the lock elements V1, V2 by closing a closing flap 3 of the base body 1, and a stopper mechanism M is thereby operated, and the stopper mechanism M connects the base body 1 to a free end block 7 of the lock element V2 so as to prevent the generation of loose-out of the base body 1 in the reverse direction to the inserting direction. The stopper mechanism M is formed of an engaging part 18 formed as a projecting hook.