To make a slope for a wheelchair land on a road surface in a proper manner.

When a parking brake is operated to let a back door 35 open, a power source is supplied to a motor drive circuit block. With the operation of a down switch, the height of a vehicle is lowered. With the further operation of the down switch, a drive motor is electrically energized during the operation of the down switch and a folding slope 13 housed being folded in a room of the vehicle is passed through an opening part of the back door to be developed outside O the vehicle room. At this point, as a free end part of the folding slope 13 contacts the road surface 11 to block the rotation of the drive motor, brushing noises generated during the rotation of the motor vanish and the waveform of a current varies while the current of the motor increases. The increase in the current is detected to stop the supply of power to the drive motor thereby halting the driving of the folding slope 13.