A parking support device is provided for extracting detection point data corresponding to a corner portion of a parked vehicle 2 from detection point data showing a series of detection points at each of which the distance to the parked vehicle 2 is detected, performing a noise component removing process and a data complementing process using a curve approximation of the series of detection points on the extracted detection point data, estimating reflection points of a detection wave in the corner portion from the detection point data and sensor position data showing a moving path of a distance sensor 3, and measuring the length of a parking space adjacent to the parked vehicle 2 according to a corner position which is determined from the positions of the estimated reflection points to determine if a vehicle 1 can be parked in the parking space.