An X-ray computed tomography apparatus includes a first X-ray tube configured to generate X-rays with which a subject to be examined is irradiated, a first X-ray detector configured to detect X-rays transmitted through the subject, a second X-ray tube which generates X-rays with which a treatment target of the subject is irradiated, a rotating mechanism which rotates the first X-ray tube, the first X-ray detector, and the second X-ray tube around the subject, a reconstructing unit configured to reconstruct an image on the basis of data detected by the first X-ray detector, and a support mechanism which supports the second X-ray tube. The central axis of X-rays from the second X-ray tube tilts with respect to a body axis of the subject. This makes it possible to reduce the dose on a portion other than a treatment target.