According to one embodiment, an X-ray tube includes an outer envelope that maintains a vacuum inside, an anode target provided inside the envelope and generating X-rays by collision of thermal electrons, and a cathode electron gun provided inside the envelope and emitting thermal electrons toward the anode target, and the X-ray tube includes an envelope assembly including a metal-made cylindrical support fixing portion and constituting the envelope, and an anode assembly including a metal-made support holding the cathode electron gun, and the support of the cathode assembly is fixed to an inner circumferential side thereof by welding.