Parking assistance method and parking assistance device

A parking assistance method comprising:

• by a sensor mounted on an own vehicle, detecting a target object around the own vehicle and a target object position, the target object position being a relative position of the target object 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, the known target object and the relative positional relationship being stored in a storage device in advance, from the storage device;
• based on a target object position detected by the sensor 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 a relative position of the target parking position;
• determining estimation precision of the estimated relative position;
• and
• 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 than a speed limit when the estimation precision is high.