A protector body is projected with lock-claw engaging frames with a spacing lengthwise, on widthwise front and rear both sidewalls. The lid is downwardly projected with lock pieces having lock claws, to be engaged with the lock-claw engaging frames, with a spacing lengthwise at both front and rear widthwise ends thereof. The lid is also projected with a vehicle-fixing bracket at any one of front and rear widthwise ends thereof. The lock-claw engaging frames of the protector body and the lock pieces of the lid, while arranged with the equal spacing on the same side with respect to a front and rear direction, are mutually different in spacing in the front and rear direction to thereby prohibit the lid. When assembled to the protector body incorrectly in a widthwise direction, lock-joining is prohibited. Thus, the vehicle-body-fixing bracket of the lid is structurally arranged in the regular direction.