An object of the present invention is to wirelessly transmit an image signal received from an in-vivo-image acquiring device via a receiving antenna to an external display device in real time and to prevent interference between the image signal wirelessly transmitted and the image signal received via the receiving antenna. A receiving device 4 according to the present invention includes a receiving unit 10 that receives an image signal from a capsule endoscope introduced into a subject via a receiving antenna a transmitting unit 14 that wirelessly transmits the image signal to an external viewer a period detecting unit 11 that detects a non-receiving period in which the receiving unit 10 does not receive the image signal and a control unit 18 that controls the constituent units of the receiving device 4. The control unit 18 estimates a non-receiving period immediately after a receiving period for the image signal based on non-receiving period information detected by the period detecting unit 11 and obtaining timing for the non-receiving period information, and causes the transmitting unit 14 to wirelessly transmit the image signal during the estimated non-receiving period.
