A cost-reduced, downsized automatic opening/closing apparatus for vehicle is achieved by reducing the number of components thereof. A case of a driving unit is provided with a drum housing portion, and a driving drum is rotatably accommodated in the drum housing portion. An electric motor is attached to the case, and the driving drum is driven for rotation by the electric motor. A cable connected to a sliding door is wound around the driving drum. By rotation of the driving drum, the sliding door is opened and closed as being drawn by the cable. The case is provided with a substrate housing portion integrally with the drum housing portion, and a control substrate for controlling an operation of the electric motor is accommodated in the substrate housing portion.