To prevent interruption of a current applied to a discharging circuit caused by contacts of a DC circuit switch and an electric motor circuit switch when a switching element of the discharging circuit is energized in stopping the operation.

When the switching element 14 of the discharging circuit 12 is conducted in stopping the operation, a control section 103 outputs a conduction command signal (d) to the switching element 14 on the condition that a contact of the DC circuit switch 4 and a contact of the electric motor circuit switch 25 are opened.