To suppress a rotation fluctuation of a rotor and a tension fluctuation of a belt.

A torque controller controls a torque loaded to the belt wound between a crank shaft of an engine mounted to a vehicle and a pulley 11 of an alternator 1, and provided with a rotation sensor (a detecting means) 14 for detecting the rotation fluctuation of the rotor 7, and a control section (a controlling means) 6 for controlling an increase or a decrease in a power generating torque of the rotor by a reverse relationship with an increase or a decrease in an inertial torque of the rotor on the basis of the rotation fluctuation.