PURPOSE: To suppress the abnormal voltage generated in making a power source by providing the high-voltage transformer of a neutral-point-switching three- phase X-ray device with a voltage-reducing means so as to reduce the single- phase supply voltage generated in making the first stage.

CONSTITUTION: A three-phase X-ray device is constituted by connecting the primary winding 12 of a high-voltage transformer, which is provided with an X- ray switching circuit 14 at its neutral point, to a tube-voltage adjusting auto- transformer 11, and rectifying the voltages of secondary windings 13 and 13' by means of a rectifier 15. On the other hand, the U.V. phase winding of the transformer 12 is provided with additional windings 12a and 12b, which are connected to the neutral point thereby forming a voltage-reducing means, which is connected to an SCR 17'. Then the SCR 17' used for making the first stage is turned on at the zero phase of the UV phase, and a second-stage SCR 18 is turned on at the peak point of the SCR 17'. As a result, the abnormal voltage generated in making a power source can be securely suppressed without using a suppressor resistor which requires control of the load condition.