A connection wire is connected to a part of a rear door popped up in a door-opening direction by an urging force. A pulley rotates responsive to a driving motor inside a wire-winding device to wind the connection wire thereon. In this manner, the rear door is automatically closed. The pulley is urged in a connection wire-winding direction by a power spring. A clutch is between the pulley and the driving motor. When the rear door is pressed by an operator's hands in a door-closing direction while the rear door is being closed, the pulley is rotated by the power spring, thus winding the connection wire thereon and preventing the connection wire from becoming loose. At this time, the connection between the pulley and the driving motor is cut off by the clutch. Thus, the pulley is rotated by the power spring freely and rapidly. In this manner, the rear door can be closed manually even while it is being closed automatically. Further, the connection wire can be prevented from becoming loose and from being sandwiched between the body of the vehicle and the periphery of a rear opening thereof.