According to one embodiment, an image generation unit generates a first image during a large aperture period and a second image during a small aperture period. An image combining unit generates a composite image based on the latest second image and the specific first image. A display unit displays the composite image in real time. A determination unit determines whether to update the first image based on an index associated with the anatomical positional shift between the first image and the second image. A driving control unit enlarges a aperture to the large aperture, when the determination unit determines to update, and maintains the aperture at the small aperture, when the determination unit determines not to update.