The present invention includes: X-ray shielding materials X-ray shielding material mounting plates to which the X-ray shielding portions are fixed a driven side link and a driving side link that connect the two X-ray shielding material mounting plates to each other so that the X-ray shielding portions face each other and cross each other connecting portions that connect each of the X-ray shielding material mounting plates to the driven side link and the driving side link and a driving device that drives the driving side link so as to rotate. Connecting portions and are provided at positions not interfering with a movable region of the X-ray shielding material mounting plates formed in conjunction with the rotational driving of the driven side link and the driving side link. The X-ray shielding material mounting plates are moved by the rotational driving of the driving side link and accordingly, the slit width between the X-ray shielding materials is changed.
