On controlling of motor rotation using an inverter, it contains harmonic components. This current harmonic distortion flows into the electric transmission and distribution system and causes troubles such as mechanical abnormality of the connected devices or AC voltage distortion. In this application, the current harmonic distortion component is analyzed by the FFT Analyzer. Capture the current fluctuation by a clamp type ammeter and perform FFT analysis of the current waveform. And then, it becomes possible to evaluate the harmonic distortion rate of high-order components in the fundamental wave and the total harmonic distortion rate.