Parking Assistance Method and Parking Assistance Device

A parking assistance method including: detecting a target object position that is a relative position with respect to the own vehicle; retrieving a known target object and a relative positional relationship between the known target object and a target parking position from a storage device; based on the detected target object position detected and a relative positional relationship between the known target object and a target parking position, estimating a relative position of the target parking position with respect to a current position of the own vehicle; based on the estimated relative position, calculating a target travel trajectory from a current position of the own vehicle to the target parking position; determining estimation precision of the estimated relative position; when the estimation precision is low, limiting a speed limit of movement speed at which the own vehicle is caused to travel along the target travel trajectory to a speed lower.