A parking assistance system includes: a color/IR detector which detects, from a camera image captured with a camera, marker candidates that are areas in each of which an intensity of a color component or an infrared (IR) component exceeds a threshold; a marker position calculator which calculates positions of the marker candidates in the camera image; and a validity verifier which determines whether the marker candidates are valid as the markers, based on the positions of the marker candidates and a predetermined positional relationship of the markers.