A parking assistance device comprising: an obstacle detection unit that detects an obstacle; a target position determination unit that determines a target position between a first virtual obstacle, which is based on a first obstacle detected by the obstacle detection unit, and a second virtual obstacle which is based on a second obstacle that is detected by the obstacle detection unit and is lined up with the first obstacle in a row in a first direction; and a route determination unit that determines a first route from the position of a vehicle to the target position when assisting a driver in parking the vehicle in a parking area, and that, in a case where while the vehicle travels along the determined first route, the obstacle detection unit has detected a third obstacle which is positioned between the first obstacle and the second obstacle and is closer to the first obstacle than the second obstacle, enlarges the first virtual obstacle toward the target position in the first direction, 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, characterized in that in a case where a distance between the first obstacle and the second obstacle in the first direction is greater than a threshold value, the route determination unit determines the second route, and in a case where the distance between the first obstacle and the second obstacle in the first direction is less than the threshold value, the route determination unit determines a third route which avoids a detected portion of the third obstacle and is set from the position of the vehicle to the target position. an obstacle detection unit that detects an obstacle; a target position determination unit that determines a target position between a first virtual obstacle, which is based on a first obstacle detected by the obstacle detection unit, and a second virtual obstacle which is based on a second obstacle that is detected by the obstacle detection unit and is lined up with the first obstacle in a row in a first direction; and a route determination unit that determines a first route from the position of a vehicle to the target position when assisting a driver in parking the vehicle in a parking area, and that, in a case where while the vehicle travels along the determined first route, the obstacle detection unit has detected a third obstacle which is positioned between the first obstacle and the second obstacle and is closer to the first obstacle than the second obstacle, enlarges the first virtual obstacle toward the target position in the first direction, 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, characterized in that in a case where a distance between the first obstacle and the second obstacle in the first direction is greater than a threshold value, the route determination unit determines the second route, and in a case where the distance between the first obstacle and the second obstacle in the first direction is less than the threshold value, the route determination unit determines a third route which avoids a detected portion of the third obstacle and is set from the position of the vehicle to the target position.