To realize the small size of a device by composing a drive transmitting member in a circular form without winding and sending.

A moving body 17 is connected to a slide door 2 to open and close the riding port of a vehicle body 1a, and assembled movable along a center track 5 out of a room. In an electric motor 8, its output shaft 8 is disposed parallel to the side surface 1c in the room. In a sprocket 10, its rotary shaft 10a is supported rotatable to be orthogonal to the side surface 1c in the room, and while it is drivingly connected to the output shaft 8a of the motor 8, a locking protrusion 10b is formed on its outer periphery. A driving tape 12 is hung on the outer periphery of the sprocket 10 in the condition locked to the locking protrusion 10b thereof, and while it is formed in a circular from being led to the room outer side from body slits 1d and 1e which are formed to vehicle bodies 1a positioning at both ends of the center track 5, it is connected to the moving body 17.