A parking assistance device includes a detection unit that detects a parkable area in a surrounding area of a vehicle, a route calculation unit that calculates a parking guidance route for guiding the vehicle from the current position of the vehicle to a parking target position contained in the parkable area, and a control unit that guides the vehicle to the parking target position according to the parking guidance route, completes the guidance when the vehicle has fit into the parkable area with a certain attitude and has reached the parking target position, and varies a completion extension period until the guidance of the vehicle is completed according to the stop mode of the vehicle when the vehicle has entered the parkable area with the certain attitude and the vehicle has stopped before reaching the parking target position.