A device controls power supplied from an inverter having a semiconductor switching element to an electric compressor having an external drive source or a built-in motor. The device includes: an apparatus for calculating a starting current value required for starting the compressor from the pressure at the discharge side circuit of the compressor; an apparatus for calculating a permitted current value of the semiconductor switching element from the temperature of the inverter installation portion; and an apparatus for comparing the calculated compressor starting current value to the permitted current value of the semiconductor switching element so as to determine whether to permit a start of the compressor.