An energisation on angle, a first energisation off angle, a second energisation off angle and a target value corresponding to an angle of rotation are determined with respect to the coil 1a on the basis of a target torque and a rotation speed. The transistors (switching element) 12a and 12b are both turned on when the energisation on angle is reached. The transistor 12a is turned off if a value of an actual current is over the target value of the current while the first energisation off angle has not been reached. The transistor 12a is turned off irrespective of the magnitude of the value of the actual current and the target value of the current when the first energisation off angle is reached. The transistors 12a and 12b are both turned off when the second energisation off angle is reached.