A parking assistance device includes: a route determination unit determining a route from an initial position of a vehicle to a target position at a time of assisting the vehicle to be parked in a parking area, wherein the route determination unit includes a first generation unit generating a first circumference being tangent to a line passing through the target position and extending along the forward direction, a second generation unit generating a second circumference being tangent to a line passing through the initial position and extending along a forward direction and to the first circumference, and a recalculation determination unit generating a third circumference having a center at the position on an obstacle in the front direction nearest to the route, and determining whether the recalculation of the route is necessary based on the first and third circumferences.