A position information estimation system includes an acquisition antenna that includes a plurality of receiving antennas and periodically acquires information from a capsule endoscope； a calculation unit (62) that calculates difference values between signal levels acquired from the plurality of receiving antennas and corresponding signal levels acquired from the plurality of receiving antennas； a determination unit (63) that compares each of the difference values with a threshold and determining whether to estimate position information； and a position information estimation unit (64) that estimates position information of the capsule endoscope when the determination unit (63) has determined that it is necessary to estimate the position information.
