Provided is a parking assistance system capable of accurately detecting the position of a vehicle relative to a parking position in the parking of the vehicle at the parking position. The parking assistance system includes: a light source 11 provided at a parking position at which a power transmission coil 3 is provided, and configured to emit light; at least two light reception units 21, 22 mounted away from each other on a vehicle 1 including a power reception coil, and each configured to receive the light emitted from the light source 11 by using a position sensitive detector 32, 34; an incident-angle calculation unit 23 configured to calculate the incident angle of the light on each of the light reception units 21, 22; a distance calculation unit 24 configured to calculate the distance between the parking position and the vehicle 1 from the incident angles of the light on the light reception units 21, 22; and a detection unit 15 configured to detect that the vehicle 1 has approached the parking position. The light volume of the light source 11 is reduced when the detection unit 15 detects that the vehicle 1 has approached the parking position.