Abstract: According to one embodiment, an X-ray tube includes an envelope including an inner space which is evacuated and is tightly closed and also including an X-ray radiation window, a cathode supporting member provided in the envelope, a cathode secured to the cathode supporting member, emitting electrons, and radiating heat, an anode target provided in the envelope, opposed to the X-ray radiation window, and radiating X-rays due to collision of the electrons emitted from the cathode, and a non-evaporable getter thermally connected to the cathode supporting member on the cathode side and activated by heat due to thermal conduction from the cathode supporting member.