Abstract: In a commutatorless motor device including a synchronous motor driven through a frequency converter including gate-controlled electric valves, and a device for detecting the phase voltages of the synchronous motor, there is a device for multiplying a signal corresponding to a stator current of the synchronous motor with the detected phase voltages. The output signal of the multiplying device is added to the output signal of the phase voltage detecting device, and the sums are passed through a logic circuit and a gate-pulse generating circuit for generating gate pulses for controlling the electric valves of the frequency converter.