A wireless power transfer system that is configured to supply electric power to a vehicle in which an electric power receiving coil capable of receiving wireless power transfer is incorporated, the wireless power transfer system comprising: a station that the vehicle is capable of entering and leaving; and at least one bottom part detection sensor having a detection unit capable of detecting an object that enters a detection range, provided at the station, and that is configured to output a bottom part detection signal corresponding to a portion, which enters the detection range, of a bottom part of the vehicle, wherein the wireless power transfer system is configured to execute: a detection signal output step in which the bottom part detection sensor outputs a time-series bottom part detection signal when the vehicle moves in the station at a predetermined speed that is a prescribed speed; and a coil position information extraction step of extracting, from the time-series bottom part detection signal, coil position information that is information about a position of the electric power receiving coil in the vehicle, characterized in that the bottom part detection sensor is a laser type distance sensor that is configured to output a bottom part detection signal corresponding to a separation distance between the portion which enters the detection range and the detection unit, and the system is configured such that the coil position information extraction step extracts, from the time-series bottom part detection signal, the coil position information based on a portion inside a contour of the bottom part of the vehicle that matches a preset contour that is a contour preset in advance. a station that the vehicle is capable of entering and leaving; and at least one bottom part detection sensor having a detection unit capable of detecting an object that enters a detection range, provided at the station, and that is configured to output a bottom part detection signal corresponding to a portion, which enters the detection range, of a bottom part of the vehicle, wherein the wireless power transfer system is configured to execute: a detection signal output step in which the bottom part detection sensor outputs a time-series bottom part detection signal when the vehicle moves in the station at a predetermined speed that is a prescribed speed; and a coil position information extraction step of extracting, from the time-series bottom part detection signal, coil position information that is information about a position of the electric power receiving coil in the vehicle, characterized in that the bottom part detection sensor is a laser type distance sensor that is configured to output a bottom part detection signal corresponding to a separation distance between the portion which enters the detection range and the detection unit, and a detection signal output step in which the bottom part detection sensor outputs a time-series bottom part detection signal when the vehicle moves in the station at a predetermined speed that is a prescribed speed; and a coil position information extraction step of extracting, from the time-series bottom part detection signal, coil position information that is information about a position of the electric power receiving coil in the vehicle, characterized in that the system is configured such that the coil position information extraction step extracts, from the time-series bottom part detection signal, the coil position information based on a portion inside a contour of the bottom part of the vehicle that matches a preset contour that is a contour preset in advance.