PURPOSE: To enable a control unit to be arranged in the suitable position in an engine room by cooling the control unit.

CONSTITUTION: A cooling device 11 is constituted of a heat absorbing piping 12 provided in a case 5 of a control unit 4, a radiating coil 13 provided in a front space 14, circulation pipings 15, 16 for connecting the heat absorbing piping 12 to the radiating coil 13, and a refrigerant 18 sealed in a circulating passage 17 formed over the heat absorbing piping 12, the radiating coil 13 and the circulation pipings 15, 16. Accordingly, since the cooling device 11 can protect respective electronic parts 8 from generated heat of an engine by repeating the evaporation in the heat absorbing piping 12 and the contraction of the radiating coil 13, and always cooling the control unit 4 through a process of radiating heat in the control unit 4 through the refrigerant 18 while circulating the refrigerant 18 in the circulating passage 17, the control unit 4 can be arranged in an engine room 2.