A device for tightening a plurality of threaded members at the same time with proper torque without necessitating a cumbersome procedure of rotating the members one by one through a specified small angle at a time and without unequivalent tightening of the members, the tightening device (1) comprises two rotary shafts (6) each provided at a forward end thereof with a wrench portion (8) fittable to the threaded member (44), motors (3) for individually driving the rotary shafts (6) and a control unit (9) for detecting the tightening torque of each threaded member (44) and controlling the motor (3) based on the detected value to ensure proper tightening, the control unit (9) checking the tightening torque of each threaded member (44) as to whether the torque is within a predetermined range and whether the difference in tightening torque between the threaded members (44) is within a predetermined range.