To enable to control regenerative current when the number of rotations of a motor becomes not less than the number of rotations of no load.

In a variable field motor, if it is determined that lead angle control is being executed in regenerative control, a core (stator) is pulled out to decrease a magnetic flux between the stator and the rotor to enable higher-speed rotation because the lead angle control corresponding to the high-speed operation is being executed. In this way, the operation for increasing the number of rotations at not less than the maximum rotation number in no load in a state where the magnetic flux is the maximum, and the regenerative processing for the higher-speed rotation state can be executed. Thus, overcharging due to over-rotation can be prevented.