To smoothly locate a top plate for placing a patient in a precise position with a small power.

The top plate 3 for placing the patient is vertically movable by a lifting device 7, and the lifting device 7 is formed of an X-arm link mechanism 24 vertically linkable and a lifting screw 47 screwed to a nut 49 the upper end of which is normally and reversely rotatably supported by the X-arm link mechanism 25 and the lower end of which is supported by the X-arm link mechanism 26 to vertically move the X-arm link mechanism 26. The lifting screw 47 is substantially vertically arranged to substantially vertically move the nut 49 by the rotation of the lifting screw 47, whereby a vertical lifting force directly acts on the X-arm link mechanism 25.