1. An in-vehicle imaging device that images a photographic subject by an imaging unit loaded on a vehicle, comprising: a detection region setting unit for setting a detection region corresponding to a predetermined object to be detected in an imaging screen, for an image signal from the imaging unit; a color signal determination unit for setting a specific color corresponding to the object to be detected and determining, in regard to pixels included in the detection region, whether color data thereof are present in the vicinity of the specific color; a gain control unit for averaging the color data of the pixels (hereinafter, approximate color pixels) that have been determined to be present in the vicinity of the specific color by the color signal determination unit concerned in the detection region, and adjusting a color gain of the image signal on the basis of a difference value between an average value of the color data of the approximate color pixels concerned and color data of the specific color; and a vehicle speed determination unit for determining a vehicle speed of the vehicle; wherein the detection region setting unit selects, based on the vehicle speed, one from a plurality of kinds of objects to be detected and sets the detection region corresponding to the selected object; and wherein the color signal determination unit selects, based on the vehicle speed, the one of the plurality of kinds of objects to be detected and sets the specific color corresponding to the selected object.