A tractor realizes the remarkable reduction of time and efforts necessary for an assembling operation of a hood. The system includes a first RF antenna for detecting signal strength of an RF signals transmit device at a first location in a vehicle and a power first detector for generating a first output signal indicative thereof. The locking mechanism includes a stop borne by the piston to provide axial locking along a direction corresponding to the mounting direction of the rod in the piston, and a washer borne by the insert or the rod.