A positioning system is configured such that an in-vehicle device includes an in-vehicle-side positioning unit that obtains in-vehicle-side positioning data that includes in-vehicle-side positioning coordinates representing positioned coordinates and a transmitting unit that transmits the in-vehicle-side positioning data obtained by the in-vehicle-side positioning unit to a portable terminal device. In addition, the portable terminal device includes a portable-side positioning unit that obtains portable-side positioning data that includes portable-side positioning coordinates representing positioned coordinates, a selecting unit that selects the in-vehicle-side positioning unit and/or the portable-side positioning unit based on a positioning environment, and a vehicle-position calculating unit that calculates a vehicle position based on positioning coordinates of a positioning unit selected by the selecting unit.