PURPOSE: To provide a high voltage generating device having a compact size, long service life and high reliability by constituting the device in such a way that a selector device for selecting an X-ray tube as an electricity feeding object is provided at the primary side of a high voltage transformer, and a plug-in structure is applied to a section for connection to the X-ray tube at the secondary side.

CONSTITUTION: Positive electrode mode units 2 and 5, and a negative electrode mode unit 6 are respectively equipped with a high voltage transformer 8 for stepping up an output signal from an inverter 7, and a rectifier for rectifying an output signal from the secondary side of the transformer 8. In addition, the units 2, 5 and 6 are respectively equipped with a plug 10 capable of coupling to the sockets of X-ray tubes 1 and 4, and a high voltage capacitor 11 for absorbing a CR time constant component, upon occurrence of an X-ray interruption signal. Also, one of the X-ray tubes 1 and 4 is selected as an electricity feeding object with a common selector switch at the pre-stage of each transformer 8 of the units 2 and 5, and negative mode units 3 and 6.