To inhibit deterioration in a battery even though a large regenerative electric power is generated.
A capacitor C is connected with a battery BT in parallel via a resistance R and charged by a regenerative electric power generated at a motor 30. An inverter 10 is connected with the battery BT in parallel and drives the motor 30. A wiring line L1 connects a positive electrode of the battery BT with one end of the inverter 10. A switch S2 includes a semiconductor switch or a mechanical switch, for example, and provided on a wiring line L2 connecting one end of the capacitor C with the one end of the inverter 10. A switch control part 20 detects whether the motor 30 is in a strenuous efforts condition or in an unloaded condition, and turns on a switch S1 and turns off the switch S2 when detecting that the motor 30 is in the strenuous efforts condition or in the unloaded condition. In addition, when detecting that the motor 30 is in a regeneration condition, the switch control part 20 turns off the switch S1 and turns on the switch S2.
YAMASHITA TOSHIRO
KOBELCO CONSTR MACHINERY LTD
Masataka Otani
Koji Nishitani