To provide an X-ray device suitable for a driving motor of a rotary anode such as an induction motor in which only a small phase angle change is measured between at a stopping state and at an operating rotary speed.

The apparatus consists of an X-ray tube 2 of a rotary anode 1, devices 11, 12 for monitoring the rotary speed of a driving motor of the rotary anode of the X-ray tube, sensor circuits 13, 14 for setting an angular signal dependent on a phase angle between a reference voltage and a current related to the motor, comparison circuits 19, 24 for detecting a change of the angular signal as a standard of the rotary speed of the motor, and a frequency converter 6. A device for forming a short keying signal 28 triggering a decrease of the frequency of the driving motor of the rotary anode is set in the apparatus.