A portable simplified image display apparatus and a receiving system are provided, which can sensuously know the state of received strength of radio signals transmitted from a body-insertable apparatus, in either case of before examination or during examination. A viewer (7) includes a detector that detects received strength of a radio signal transmitted from a capsule endoscope (2) and a notifying unit that notifies the detected state of received strength in a display pattern such as a picture display of a capsule (41). Therefore, in either case of before examination or during examination, the state of received strength of radio signals transmitted from the capsule endoscope (2) can be sensuously known according to the notification result of the state of received strength. If it is during examination, supplementary observation can be performed based on an excellent received image by searching a site having strong received strength, thereby enabling contribution to satisfactory examination.