A movable diaphragm unit is configured such that, when a restricting blade is moved away from a normal line extending from a center of a focal spot of X-ray to a first virtual plane including a detector plane, a moving distance of a crossing line of a second virtual plane including an end surface of the restricting blade and a third virtual plane including the focal spot with respect to a center of the focal spot becomes shorter than a moving distance with respect to the normal line of the end surface.
