An object of the present invention is to alleviate an image diagnosing work in a work station or the like. In a viewer 7 for displaying, on a display unit 11, image data based on a radio signal transmitted from a capsule endoscope to be inserted into a subject, an image processing circuit 35 processes image data received from a receiving apparatus 5 via an interface 34, so as to produce an image processing result of the image data, and further, a control unit 38 displays the image and the image processing result on the display unit 11 in real time, so as to enable a body-cavity image to be observed with reference to the image processing result.