Parking assistance device and method used therefor

A parking assistance device capable of performing an easy operation for parking a driver's own vehicle along a parking course up to a parking target position. A parking course in which the driver's own vehicle reaches a parking target position indicated by a marker of a screen of a display of the driver's own vehicle is calculated up (S16). If a steering operation of the driver's own vehicle is performed, in the case that the current rudder angle changes towards a target rudder angle in order to move the driver's own vehicle along a parking course. the steering assistant power of the driver's own vehicle is increased (S21) and thus the steering operation of the driver's own vehicle is performed by a relatively small operational power. On the other hand, if the current rudder angle changes away from the target rudder angle, the steering operation of the driver's own vehicle is performed by a relatively large operational power since the rudder supplementary power is decreased (S21).