Provided is a narrow docking mechanism that enables a bed and an apparatus main body to be coupled together with sufficient holding force during docking and that does not hinder access by an examiner to an object. A coupling mechanism on a bed 3 side includes a coupling plate 7 having one end fixed to the bed 3, and a coupling mechanism 50 on the main apparatus side includes a plurality of rollers 12 arranged side by side along the shape of both sides of the coupling plate 7. As the plurality of rollers 12 sandwiches and holds the coupling plate 7 from both sides, the coupling plate 7 can attach to and detach from the bed 3 by coupling the bed to the apparatus main body so as to be inserted between the arranged rollers 12.