According to one embodiment, a holding apparatus includes an arcuated arm, a first roller, and a second roller. The arcuated arm is provided with a guide groove along the outer surface, has a hollow portion inside, and holds the X-ray generator and X-ray detector while making them squarely face each other. The first roller runs in the hollow portion in contact with the inner wall of the hollow portion on the outer surface side. The second roller runs in the guide groove while being fitted in the guide groove, and holds the arm together with the first roller so as to allow the arm to slide along the arcuated direction.