To prevent the dispersion of the torque at a motor side by detecting each peak of the load torque generated as the reaction when the torque at motor side is transmitted to an impact mechanism, and controlling the operation of motor for enabling the peak to be agreed with a peak of the torque ripple of the motor.

This power impact tool comprises a SR motor 1 and an impact mechanism 2, and executes the screwing and the like by converting the average rotational energy of the motor 1 into the torque for a short time. On this occasion, a sensor 4 is mounted for successively detecting a position of a rotor of the motor 1, and the motor 1 is switched ON and OFF by a signal output from the sensor 4 to an inventor 3. An output signal of the sensor 4 is output to a speed amplifier 8 through a F/V converting part 5, and the deviation with respect to an output signal from a torque adjustment part 7 is determined. Each peak of the load torque is detected an control part 6, and the motor 1 is controlled so that the peak is agreed with a peak of the torque ripple of the motor 1.