With the automatic bypass sequence (Pr.139 ≠ 9999, Pr.159 = 9999), the motor operation is switched to commercial power supply operation when the output frequency reaches Pr.139 and the inverter is used only for the acceleration/deceleration operation. With the automatic bypass sequence (Pr.139 ≠ 9999, Pr.159 = 9999), the motor operation is switched to commercial power supply operation when the output frequency reaches Pr.139. When the frequency command becomes less than the difference between Pr.139 and Pr.159, it is automatically switched to inverter-driven operation at the frequency by the frequency command. Therefore, use the commercial power supply for high-speed operation, and inverter for low-speed operation.