Disclosed herein is a technique of deriving a parking trajectory for a vehicle. In the technique, a first extension straight line, which includes a linear travel path of the vehicle when the vehicle initially goes in reverse from a neutral position of a steering angle, is calculated upon the vehicle being to go in reverse. A final parking location is obtained based on a calculated length of a parking space and a parking target location in the parking space, and a second extension straight line which includes the final parking location is calculated therefrom. When the vehicle going in reverse along the first extension straight line turns and goes in reverse towards the second extension straight line, an intermediate extension straight line connecting the first extension straight line and the second extension straight line is calculated so that the vehicle is aligned with the second extension straight line.