1. A face region estimating device for estimating a person's face region contained in a plurality of picked-up images from the picked-up images taken of a mobile body by a plurality of cameras, comprising; a distance information generating unit for generating a distance to the mobile body as distance information, based on an azimuth difference of the plurality of picked-up images; a motion information generating unit for generating motion of the mobile body as motion information, based on a difference of the picked-up images inputted in time series from at least one of the plurality of cameras; an object distance setting unit for setting an object distance in which the mobile body exists, based on the distance information and the motion information; an object distance image generating unit for generating an object distance image composed of pixels corresponding to the object distance, based on the distance information; an object region setting unit for setting an object region containing the region of the mobile body, corresponding to at least the object distance set by the object distance setting unit in the object distance image; an outline extracting unit for extracting an outline from the object region set by the object region setting unit; a head region setting unit for setting a head region assuming the mobile body to be a person, based on a pixel distribution of the object distance image corresponding to a predetermined range on the basis of a pixel position at the upper part of the outline extracted by the outline extracting unit; and a face region extracting unit for extracting the person's face region from the picked-up image, based on the color distribution of the picked-up image corresponding to the head region set by the head region setting unit, wherein the face region extracting unit comprises an HLS threshold value setting unit for setting upper and lower limit values of hue, saturation, and lightness ranges in which the total of the pixels corresponding to each of the values is the largest in the predetermined range for every value of hue, saturation and lightness value in the head region, as hue, saturation, and lightness threshold values, respectively, wherein a region composed of the pixels contained in the ranges of the hue, saturation and lightness threshold values is provided as the face region, and an RGB threshold value setting unit for setting the upper and lower limit values of red, green, and blue ranges in which the total of the pixels corresponding to the concentration value is the largest in the predetermined range for every concentration value of red, green and blue, as three primary colors of light in the head region as red, green, and blue threshold values, respectively, wherein the region composed of the pixels contained in the ranges of the red, green, and blue threshold values is set to the face region when the saturation threshold value is or below a predetermined value, and wherein the region composed of the pixels contained in the ranges of the hue, saturation, and lightness threshold values is set to the face region when the saturation threshold value is greater than the predetermined value.