Abstract: An image processing device 3 is comprised of an image information acquiring unit 31, a variation calculating unit 32, and an environment detecting unit 34. The image information acquiring unit 31 continuously acquires an image of an object on a lateral side of a vehicle at predetermined sampling time intervals, the image being captured by each of cameras 2a and 2b mounted on the vehicle. The variation calculating unit 32 calculates an image variation from at least two images acquired by the image information acquiring unit 31. The environment detecting unit 34 detects a traveling environment in an area surrounding the vehicle from the image variation calculated by the variation calculating unit 32.