Between terminals of secondary windings in a high-voltage transformer (3), there are connected in parallel input side terminals of a plurality of diode full bridge circuits each via voltage maintaining means such as a capacitor maintaining a voltage peak value for a longer period than the cycle of an inverter (2). Between the input side terminals of the diode full bridge circuits, there are connected voltage maintaining means such as capacitors maintaining a voltage peak value for a longer period than the cycle of the inverter. Moreover, the output side terminals of the diode full bridges are connected in series via smoothing means such as almost equivalent smoothing capacitors and between the output side terminals, an anode grounding type X-ray tube (5) is connected. Thus, it is possible to realize a small-size and light-weight device at a reduced cost and reduce the ripple in the output voltage while using the anode grounding type X-ray tube.