A receiver receives in-vivo information on the body of a patient through a receiving antenna through a receiving antenna after a pill 1 is inserted into the body of the patient and acquires the in-vivo information on the body of the patient. The pill 1 receives a power-supply signal supplied from the receiver through a power receiving antenna 17, and a power recovering circuit 19 recovers the power-supply signal as electric power. A level determining circuit 20 compares the power recovered with a predetermined value to determine the strength of the power-supply signal as a determination result signal based on the result of comparison, and wirelessly transmits the determination result signal to the receiver.
