A parking assistance device includes: an acquisition unit that acquires a first distance between a vehicle and a first obstacle measured by a distance measuring unit and a second distance between the vehicle and a second obstacle measured by the distance measuring unit; a calculation unit that calculates an inter-objects distance between the first and second obstacles; and a generation unit that generates a guidance route for the vehicle such that each of the first and second distances become equal to or longer than a second reference distance which is shorter than a first reference distance that is a reference for safe travelling of the vehicle, when the vehicle is caused to move between the first and second obstacles and within the inter-objects distance and in a case where a condition is satisfied.