PURPOSE: To provide a system for switching a PM motor automatically and synchronously from one of a plurality of inverters to another inverter in which the synchronous switching can be effected quickly and positively in safety even upon variation of the r.p.m. of motor.

CONSTITUTION: The periods of output signals (f) from inverters 1, 2 are matched under a state where a PM motor 4 is driven by an inverter 1. The inverter 2 is then waited temporarily and a synchronism matching signal is delivered in order to switch the connection of the PM motor 4 to the inverter 2 side. When a voltage is induced in the PM motor 4 and the period and phase thereof match those of an output signal from the inverter 1, operation of the inverter 2 is resumed while matching the period and phase with those of the voltage induced in the motor.