PURPOSE: To rearrange detection surfaces on the same horizontal plane and to obtain a long detection surface by constituting plural radiation detectors so that their detection surfaces can be expanded on the same plane around axes.

CONSTITUTION: The radiation detectors 3 are arranged contiguously so that the detection surfaces form a triangle from the end surface of a rotary disk 2 which is racked freely rotatably on a main body 1 and has a horizontal rotational axis. One of the detector 3 is fixed to the disk 2 by a fixed arm 4 fixed to the disk 2 and detectors 3 are coupled freely rotatably with both sides of the one detector through hinges 5 at their adjacence parts. When the head or abdomen is measured partially, the part is positioned inside the polygon while the detectors 3 form the polygon. When the whole body is measured, the detectors 3 are expanded on the same horizontal plane and the human body is laid on the top surface.