A seatbelt retractor integrated with an electronic control unit. A motor is disposed above both side walls of a frame and on the same side as a spool with respect to a back board. The motor is detachably fixed to at least one of the back board and the both side walls and of the frame. The ECU is detachably mounted to an upper stay extending upward from the back board of the frame and to be mounted to the vehicle body. In this manner, the motor and the ECU are integrated with a seatbelt retractor. Since the ECU is mounted to the upper stay, the weight of the ECU is dispersed not only to the main body of the seatbelt retractor but also to the upper stay. Thus, the vibration of the seatbelt retractor may be reduced.