PURPOSE: To easily determine what region of an examinee lesion is present in, by displaying a slice converting image and the fluoroscopic image of an examinee in a superposed state.

CONSTITUTION: A memory means 10 stores a plurlaity of the slice images and scannoimages of an examinee collected by an X-ray CT scanner. A slice converting processing part 11 has the first and second buffers 15, 17, an interpollation processing means 18 and a scale adjusting means 19 and forms a desired slice converting image from a plurality of the slice images in the memory means 10. A synthesizing processing means 12 synthesizes the slice converting image obtained by the slice converting processing part 11 and the scannoimage in the memory means 10 and sends out the processing result to a display means.