A rear gate is constructed to be opened and closed by a driving unit installed on a vehicle body side, and the driving unit is constructed to have a motor which can rotate both in normal and reverse directions, a gearbox to which a pinion is pivotally attached for reducing the rotating speed of the motor for output, and a rack adapted to reciprocate in directions normal to an axial direction of a hinge shaft by virtue of the rotation of the pinion and connected to the rear gate at one end thereof. An electromagnetic clutch for connecting and disconnecting a power transmission path between an output shaft of the motor and the pinion is provided in the interior of the gearbox, so that the rack is disposed above or below the gearbox at a position directly above or below the clutch.