A parking aid system is disclosed. The parking aid system includes: a parking space borderline recognition section configured to recognize two borderlines of the parking space based on a captured image, which is captured by an imaging device mounted to the vehicle, the two borderlines respectively being two parts of the parking space boundary opposite to each other in a width direction of the parking space; a displacement calculation section configured to calculate displacement of the vehicle in the width direction with respect to the two borderlines based on positions of the two borderlines in the captured image and an imaging range of the imaging device; and a notifier configured to notify the displacement calculated by the displacement calculation section.