To further reduce the size, weight and cost, by efficiently cooling a heating part on an inverter circuit board for constituting an inverter control means.

An inverter base board 28 for mounting the heating part 26 for constituting the inverter control means 9 on the reverse surface side of the base board, is stored in a case 30 composed of a material superior in heat conductivity so that the heating part 26 is brought into close contact with a bottom surface of the case 30, and the case 30 is arranged downward so that the bottom surface becomes an upper part on at least any one lower side of an electric motor 2 and compressors 3 and 4 between a pair of air tanks 5 and 6 arranged in parallel at an interval. The heating part 26 is cooled via the case 30 by guiding an air flow along the bottom surface of the case 30 by cooling fans 20 and 21 driven by the electric motor 2.