A stack of many stimulable phosphor sheets and an X-ray tube are positioned with an object intervening therebetween, and moved with respect to each other around a tomographic plane in the object so as to satisfy the linear rule and the geometric rule in the course of exposure of the object to X-rays, thereby storing images of many tomographic planes in the stimulable phosphor sheets in a single recording step. The respective stimulable phosphor sheets are then exposed to a stimulating ray to cause them to emit light, the emitted light is photoelectrically read out, and the obtained electric signals are reproduced as visible tomographic images usable in diagnosis with high efficiency and accuracy. The electric signals may be superposed one upon another and reproduced as an X-ray image of any slice thickness, particularly a slice thickness of 5 mm or more, which is free from interfering shadows.