According to one embodiment, an X-ray tube includes a cathode, an anode, a cathode hood, a first X-ray transmission window, an envelope, and a first restraining member. A second side surface of the first restraining member has a contact surface that is pressed against an inner wall surface in a first hole of the cathode hood. The first X-ray transmission window is maintained in a state of being restrained to an overlap space of a first bottom surface in the first hole by the first restraining member.