To prevent belt clamping force of a pulley from becoming temporarily excessive right after ignition-off.

It is determined whether or not an indicated current value As1 during ignition-off is higher than a predetermined standby current value A2 when the ignition-off is executed (ST1:YES), an indicated current value As is swept down to a predetermined standby current value A2 (ST3) to keep it at the standby current value A2 (ST4) when the indicated current value As1 is determined to be higher (ST2:YES), and sweeps the indicated current value As down to zero again after an engine is stopped and a predetermined time elapses (ST6). On the other hand, the indicated current value is kept (ST5) when the indicated current value during the ignition-off is not higher than the predetermined standby current value (ST2:NO), and the indicated current value As is swept down to zero after the engine is stopped and the predetermined time elapses (ST6).