An image processing device applied to a driving assistance system, which includes: a driving assistance device that detects a relative position of a lane marking with respect to a vehicle and assists a driving of the vehicle based on a detected positional information; and a head-up display device that projects a display image on a projection area arranged on the vehicle to visually recognize a virtual image of the display image, includes: an acquisition device that acquires the positional information; and a generation device that generates the display image including a predetermined display element. The generation device generates the display image to visually recognize the display element at a position associated with the positional information and to visually recognize the display element as a shape inclined toward the vehicle from the lane marking.