According to one embodiment, an X-ray tube includes an anode including a target surface, and a cathode including a first filament and a focusing electrode. The focusing electrode includes a valley bottom portion, a first inclined plane sloping up from the valley bottom portion in a direction of the anode, a first focusing groove, and a first storage groove. θ1 is greater than 0°. The first focusing groove has a longitudinal axis. One end portion on the first extension line side of the first focusing groove is closer to a first reference surface than the other end portion of the first focusing groove.