According to one embodiment, an X-ray tube includes an elongated anode target, a cathode, and a vacuum envelope. The cathode includes an electron emission source and a converging electrode including a trench portion. The trench portion includes a closest inner circumferential wall, an upper inner circumferential wall, and a lower inner circumferential wall. The electron emission source projects towards a opening of the trench portion from a boundary between the closest inner circumferential wall and the upper inner circumferential wall.