The present embodiments improve the radiation monochromy of an x-ray device with a control electrode for controlling a flow of electrons generated between a cathode and an anode. A correction voltage is generated in accordance with a correction function. This correction voltage is used for correction of a voltage applied between the anode and the cathode in terms of a constant voltage, even in the period of control using the control electrode. The voltage applied between the anode and the cathode is corrected with the generated correction voltage.