An image obtaining method and apparatus for an endoscope apparatus wherein reductions to the gradations of the image data borne by the analog signal are suppressed and digital values having a narrower dynamic range are obtained when the photoelectrically converted and outputted analog signal is converted to digital values. The insulative housing defines a substantially rectangular cavity in a middle thereof adapted for receiving an electronic package therein. A central group of the read-out elements is located in a central region of the x-ray detector and a peripheral group of the read-out elements is located in a peripheral region which surrounds the central region.