PURPOSE: To enable the fastening of bolt under the condition that the upper part of a collision sensor is temporarily locked to facilitate the fitting structure by providing a hook part in the upper side of a collision sensor, and providing a bolt fastening part in the lower side thereof, and hooking the collision sensor on a hook part of the fixed member side inside of a side door, and thereafter, fastening the sensor to a base plate.

CONSTITUTION: A hook part 16a is provided in the upper side of a collision sensor 11, and a bolt fastening part 16b is provided in the lower side thereof. Furthermore, a hook part 15a, on which the hook part 16a of the collision sensor 11 is hooked, and a fastening base plate 15b to be fastened with the fastening part 16b by a bolt 17 under the hooking condition are previously fitted to a fixed member 15. Next, the hook part 16a is hooked on the hook part 15a to lock the collision sensor 11 at the fixed member 14 temporarily, and thereafter, the collision sensor 11 is fastened by the bolt 17.