A parking assistance device assists in re-parking a vehicle that has been parked with its position and orientation deviated from ideal ones, by repositioning the vehicle to be at a correct position and in a correct orientation. A parking assistance device is adapted to assist in parking a vehicle in a parking space provided on one side of a road, and includes a parking path setting unit that sets a parking path of from the initial position of the vehicle on the road to a target parking position in the parking space, a positional deviation determination unit that determines whether there is any positional deviation between the vehicle and the parking space when the vehicle has been parked along the parking path, and a repositioning path computing unit configured to compute a repositioning path when a positional deviation is determined to be present.