A sliding door slides along the side of a vehicle. An electric drive unit is disposed on a floor of the vehicle and a lower guide rail is disposed under the floor. A lower roller bracket coupled to the sliding door moves along the lower guide rail back and forth. A door-opening outer tube mounted to the sliding door extends from the electric drive unit to a rear wire guide at the rear end of the lower guide rail. A door-closing outer tube extends from the electric drive unit to a front wire guide at the front end of the lower guide rail. A door-opening wire extends through the door-opening outer tube from the electric drive unit to the lower roller bracket. A door-closing wire extends through the door-closing outer tube from the electric drive unit to the lower roller bracket.