When a slide door stops at an intermediate position over a protection action time start time (T.beta.), an electric motor is operated in closing direction in low driving force mode. When the move speed (Vc) of the slide door is a movable speed (V.alpha.) or higher, the slide door is moved to its fully closed position by automatic closing action, and an electromagnetic clutch is disconnected. On the other hand, when the move speed (Vc) of the slide door is not made to reach the movable speed (V.alpha.) or higher over a speed judgment time (Tj), the electric motor is operated in closing direction in the low driving force mode, and when the move speed (Vo) of the slide door is made to reach the movable speed (V.alpha.) or higher, the slide door is automatically opened. Further, when the move speed (Vo) of the slide door is made to reach the movable speed (V.alpha.) or higher for the speed judgment time (Tj), the electric motor is stopped, and the electromagnetic clutch is made into its disconnected status.