A parking assistance device includes: an obstacle detection unit detecting an obstacle; a target position determination unit determining a target position between a first virtual obstacle, based on a first obstacle, and a second virtual obstacle based on a second obstacle being lined up with the first obstacle in a first direction; and a route determination unit determining a first route from the position of a vehicle to the target position, and that, when while the vehicle travels along the determined first route, the obstacle detection unit has detected a third obstacle positioned between the first and second obstacles and closer to the first obstacle than the second obstacle, enlarges the first virtual obstacle, and determines a second route that avoids the enlarged first virtual obstacle and is set from the position of the vehicle to the target position.