The entire amount of seatbelt webbing can be securely wound even when a winding force of a spring cannot be efficiently utilized. When a belt winding speed of a spool (4) by spring means (14) is larger than a predetermined value, a winding speed V S , which is input in a motor-power transmission device (5) from the spool (4), is larger than a winding speed V M , which is input in the motor-power transmission device (5) from a motor (10) (V S > V M ). At this time, the motor-power transmission device (5) is turned off so that the winding of the seatbelt webbing (3) is performed by the spring means (14). When the belt winding speed of the spool (4) by the spring means (14) is not more than the predetermined value so as to be V M > V S , the motor-power transmission device (5) is turned on so that the winding of the seatbelt webbing (3) is performed by power of the motor (10). Even when a winding force of the spring cannot be efficiently utilized, the entire amount of seatbelt webbing can be securely wound by power of the motor (10).