1. An image tracking device comprising: a video camera for taking an image in front of a vehicle: a memory for memorizing an image signal outputted by the video camera; image processing means for recognizing and tracking a plurality of vehicles by processing the image signal memorized in the memory; image display means for displaying the image outputted by the video camera and data outputted by the image processing means; white line sampling means for sampling a white line of a road; means for determining, based on the white line data sampled by the white line sampling means, which one of said plurality of vehicles running within a range of a lane of a driving vehicle is to be tracked as a target vehicle, and which one of said plurality of vehicles is to be tracked as a cut-in vehicle running between the target vehicle and the driving vehicle; and means for releasing a tracking window when at least a portion of another vehicle overlaps the target vehicle, whereby the overlapping vehicle may then be tracked as the target vehicle.