an x - ray detecting element detects an image produced by x - ray irradiation . an apparatus case capable of being inserted into a mouth has an x - ray irradiation face having different dimensions in two directions perpendicular to each other , and houses the x - ray detecting element . a cable is connected to the apparatus case to transmit a signal from the x - ray detecting element to the outside of the apparatus case . the cable is drawn out from the apparatus case in a direction which is parallel with the x - ray irradiation face and perpendicular to the longitudinal direction of the x - ray irradiation face . according to this configuration , the cable does not obstruct the imaging operation in a course of imaging teeth in a mouth , particularly a molar portion . therefore , an imaging operation can be easily conducted without giving the subject an unpleasant feeling .