The supporter supports a patient and is disposed movably along the body axis direction of said patient. The imaging part includes an X-ray-generator and an X-ray-detector. The X-ray-generator irradiates X-rays while rotating around the body axis. The X-ray-detector detects the X-rays that have permeated the patient. The collimator changes the irradiation field of the X-rays to be irradiated. The scan controller controls the movement of the supporter and the imaging part. The image-reconstructing part reconstructs image data based on the X-rays that have been detected by the X-ray detector. The movement amount-detector detects the amount of movement of the patient by the supporter. The collimator controller controls so as to change the size of the opening of the collimator based on the amount of movement.