A position information estimation system includes: a body-insertable apparatus that is inserted into a subject and moves through an inside of the subject; a receiving unit that receives information from the body-insertable apparatus; and an information processor that performs processes on the information acquired from the receiving unit. The receiving unit includes an acquisition antenna that includes a plurality of receiving antennas and acquires information from the body-insertable apparatus. The information processor includes: a calculation unit 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 that compares each of the difference values with a threshold and determining whether to estimate position information; and a position information estimation unit that estimates position information of the body-insertable apparatus when the determination unit has determined that it is necessary to estimate the position information.