An opening and closing device opens and closes a sliding door by using a cable connected to the sliding door movably attached to a vehicle body. The opening and closing device has a base bracket, a motor, a transmission, a rotary drum, a first conduit fixed portion, a second conduit fixed portion, a first tension controller and a second tension controller. The base bracket is fixed to the vehicle body with bolts. The motor, the transmission, the rotary drum, the first and second conduit fixed portions and the first and second tension controllers are fixed to a disposition face of the base bracket. The first and second tension controllers are respectively disposed between the rotary drum and the first conduit fixed portion and between the rotary drum and the second conduit fixed portion, and applies tension to the cable fed from the rotary drum to take up the slack.