A receiver system comprising: a capsule endoscope that is configured to be introduced into a subject and transmit an in-vivo information signal including an in-vivo image characterized by a plurality of wireless relay devices that are disposed on an outer surface of the subject, are configured to receive the in-vivo information signal transmitted by the capsule endoscope, and are capable of transmitting at least one of the in-vivo information signal and a received electrical field intensity signal that is measured by using the in-vivo information signal; and a receiving device that is located outside of the subject and is configured to receive the in-vivo information signal transmitted by the wireless relay devices, wherein each of the wireless relay devices includes an interior side receiving unit (R1 that is configured to receive the in-vivo information signal transmitted by the capsule endoscope at a first frequency; an exterior side transmitting unit that is configured to transmit the in-vivo information signal at a second frequency; an exterior side receiving unit that is configured to receive a control signal transmitted by the receiving device at the second frequency; and a control unit that is configured to control transmissions and receptions by the interior side receiving unit and the exterior side transmitting unit based on the control signal, wherein the receiving device is configured to transmit a polling signal to each of the wireless relay devices, each of the wireless relay devices is configured to transmit the received electrical field intensity signal to the receiving device when receiving the polling signal, the receiving device is configured to select, based on each of the received electrical field intensity signals, a desired wireless relay device from the wireless relay devices and transmit a selection signal to the selected wireless relay device, the control unit in each of the wireless relay devices is configured to determine, when receiving the selection signal from the receiving device, whether the selection signal is addressed to the wireless relay device itself, and the control unit is configured to transmit, when determining that the selection signal is addressed to the wireless relay device itself, the in-vivo information signal received by the interior side receiving unit to the receiving device via the exterior side transmitting unit. a capsule endoscope that is configured to be introduced into a subject and transmit an in-vivo information signal including an in-vivo image characterized by a plurality of wireless relay devices that are disposed on an outer surface of the subject, are configured to receive the in-vivo information signal transmitted by the capsule endoscope, and are capable of transmitting at least one of the in-vivo information signal and a received electrical field intensity signal that is measured by using the in-vivo information signal; and a receiving device that is located outside of the subject and is configured to receive the in-vivo information signal transmitted by the wireless relay devices, wherein each of the wireless relay devices includes an interior side receiving unit (R1 that is configured to receive the in-vivo information signal transmitted by the capsule endoscope at a first frequency; an exterior side transmitting unit that is configured to transmit the in-vivo information signal at a second frequency; an exterior side receiving unit that is configured to receive a control signal transmitted by the receiving device at the second frequency; and a control unit that is configured to control transmissions and receptions by the interior side receiving unit and the exterior side transmitting unit based on the control signal, wherein an interior side receiving unit (R1 that is configured to receive the in-vivo information signal transmitted by the capsule endoscope at a first frequency; an exterior side transmitting unit that is configured to transmit the in-vivo information signal at a second frequency; an exterior side receiving unit that is configured to receive a control signal transmitted by the receiving device at the second frequency; and a control unit that is configured to control transmissions and receptions by the interior side receiving unit and the exterior side transmitting unit based on the control signal, wherein the receiving device is configured to transmit a polling signal to each of the wireless relay devices, each of the wireless relay devices is configured to transmit the received electrical field intensity signal to the receiving device when receiving the polling signal, the receiving device is configured to select, based on each of the received electrical field intensity signals, a desired wireless relay device from the wireless relay devices and transmit a selection signal to the selected wireless relay device, the control unit in each of the wireless relay devices is configured to determine, when receiving the selection signal from the receiving device, whether the selection signal is addressed to the wireless relay device itself, and the control unit is configured to transmit, when determining that the selection signal is addressed to the wireless relay device itself, the in-vivo information signal received by the interior side receiving unit to the receiving device via the exterior side transmitting unit.