PROBLEM TO BE SOLVED: To provide "a GPS reliability determination device" capable of obtaining a highly reliable determination result in a case where high reliability is fundamentally predicted even when a result is determined to be low reliability.SOLUTION: A GPS reliability determination device includes: reference relative position acquisition means (S15) for acquiring, as a reference relative position, a relative position between a GPS position acquired by a GPS position detection system and a reference position based on an autonomous navigation position when reliability of the GPS position is determined to be high; low-reliability relative position acquisition means (S20) for acquiring, as a low-reliable relative position, a relative position between a GPS position acquired by a GPS position detection system and a reference position based on an autonomous navigation position when reliability of the GPS position is determined to be low; and reliability correction means (S21, S22) for correcting, to highly
