A voltage control section for controlling a pulsed acceleration voltage applied between a photoelectron releasing layer and an X-ray target in order to accelerate a photoelectron is further provided, so that the acceleration voltage is maintained at a pulse top voltage until the X-ray target is bombarded with the photoelectron after the photoelectron is released from the photoelectron releasing layer. The pulse width of acceleration voltage can be set narrower to such an extent that no discharge occurs, which enables the pulse top voltage to become higher, whereby the energy of pulse X-rays can be made higher by enhancing the speed of photoelectrons.