An automatic opening/closing apparatus for vehicle is downsized, and cost of the automatic opening/closing apparatus is reduced by reducing the number of its components. A driving drum is rotatably accommodated in a main body case of a driving unit, and one ends of cables are connected to a sliding door and the other ends are wound around the driving drum. An electric motor is attached to the main body case, and the driving drum is driven for rotation. A tensioner mechanism applying a predetermined tension to the cables is accommodated in the main body case. A control device, including a control substrate and a substrate case for accommodating the control substrate, is disposed to be overlapped on an axial-directional side of the driving drum to a portion of the main body case for accommodating the tensioner mechanism, whereby an operation of the electric motor is controlled by the control device.