An X-ray collimator for controlling an X-ray radiation field, having a lower base member, a pair of regulating members, a pair of surrounding members having substantially U-shaped forms in planar view, N columnar members surrounded by the pair of surrounding members (where N is 4, 6, or 8), a guiding member, a pair of moving members moving parallel to the opposed surfaces of the regulating members, an upper base member, a first motor for horizontally moving the pair of moving members, and a second motor for moving the columnar members. The first motor is driven to horizontally move the pair of moving members over the same distance in opposite directions. The second motor is configured to move one of the columnar members along an internal surface of the surrounding member surrounding the columnar member, thereby moving the other N−1 columnar members sequentially.