A parking assistance device includes: an obstacle detection unit that detects an obstacle; a separated distance determination unit that determines a separated distance between the obstacles when a plurality of the obstacles are detected; a target position determination unit that determines a target position in a guidance route; a route calculation unit that calculates the guidance route; and a control unit that guides a vehicle in accordance with the guidance route, wherein, when a second obstacle is detected in a second direction orthogonal to a first direction in which one or plurality of first obstacles extends or are lined up while being separated from each other and at a position separated from the first direction, the separated distance determination unit determines the separated distance between the first and second obstacles.