An inverter device in the present invention comprises a three-phase inverter (2) for converting DC electric power into AC power for supplement to an AC electric motor (3) and a control device (4 - 11) operatively associated therewith, and said control device includes a phase current detection section (7, 8) for outputting a phase current waveform based on a DC input current and an operational processor section (4 - 6, 10, 11) for performing based on said phase current waveform operational processing for control of said inverter device. Thereby, the inverter device can be constructed to be very compact.