A high voltage generation apparatus according to an embodiment includes power factor improvement circuitry and gain adjustment circuitry. The power factor improvement circuitry improves a power factor of alternating current (AC) power output from an AC power source in order to supply an X-ray tube with power that is controlled based on a reference voltage. The gain adjustment circuitry is included in the power factor improvement circuitry, and adjusts a gain of an output voltage relative to the reference voltage so that the gain differs between a first period including a start of irradiation of X-rays by the X-ray tube or an end of irradiation of X-rays by the X-ray tube, and a second period different from the first period.
