A mobile station transmits a first radio signal, a reference station transmits a second radio signal. Fixed stations extract phase differences (Δφmf1) to (Δφmf3), respectively, between a carrier included in the first radio signal and reference clocks of the respective fixed stations. The fixed stations extract phase differences (Δφsf1) to (Δφsf3), respectively, between a carrier included in the second radio signal and the reference clocks of the respective fixed stations. A server cancels phase offsets (φf1) to (φf3) of the respective fixed stations using phase difference information between the mobile station and each of the fixed stations and phase difference information between the reference station and each of the fixed stations, obtains distance information between each of the fixed stations and the mobile station, and calculates a position of the mobile station.