A parking position adjustment device that assists in correctly changing a parking position within a parking space in which a vehicle has already parked is provided.The parking position adjustment device includes: a current position setting unit that sets the position in which a vehicle is already parked as a current position; a parking space specification unit that specifies a parking space, in which the vehicle is parked, that includes the current position; a target parking position setting unit that sets, within the parking space, a target parking position to which the vehicle is to be moved from the current position; and a movement path calculation unit that calculates a movement path of the vehicle from the current position to the target parking position.