An X-ray computed tomography apparatus according to an embodiment includes an X-ray tube, a bias power supply, and an X-ray control unit. The X-ray tube includes a cathode, an anode, and a grid between the cathode and the anode. The bias power supply generates a bias voltage to be applied to the grid to control a tube current between the cathode and the anode. The X-ray control unit applies a bias voltage as a pulse string for generating a constant tube current and controls at least one of the pulse count and pulse width of a bias voltage for each predetermined period.
