To prevent the occurrence of an artifact by sticking a radiation quality converting sheet to an array detecting equipment which consists of several kinds of attenuating elements arrayed in a prescribed pattern, and which attenuates X-rays by prescribed different rate in a device picking-up an image by using radiation with different level of energy.

The X-rays exposed in an X-ray generating device 1 are converted into an object transmission signal by the radiation quality converting sheet 4 which is stuck to an array detecting equipment 3 and which consists of the array of the several kinds of attenuating elements in a prescribed pattern, and which attenuates X-rays by prescribed different rate so that an X-ray signal is detected at every pixel by the array detecting equipment 3. That is, the radiations with different level of energy, which are respectively attenuated by the several attenuating elements of the sheet 4, are detected by corresponding detecting elements and the signals are digitized. Then the digitized signals are transferred to an image processor 5, stored in an image memory 6, image- processed by an arithmetic circuit 8, and then, image-displayed in a display device 9.