1. A stereo camera apparatus which measures a distance to a three-dimensional object, using two images picked up by two cameras, comprising: an image capture unit which takes in the two images; an image generating unit which changes resolution of a partial area of each image taken in by the image capture unit; and a distance calculating unit which calculates a distance from the vehicle to a three-dimensional object that is imaged in the partial area, based on disparity of the partial area of each image in which resolution is changed by the image generating unit; wherein the image generating unit changes the resolution of the partial area of each image based on the distance from the vehicle to the three-dimensional object, such that a number of pixels in which the three-dimensional object is included becomes a number of pixels that is preset according to a structural type of the three-dimensional object; and wherein the image generating unit changes the resolution to a higher resolution when the distance from the vehicle to the three-dimensional object is longer than a preset first standard distance, and the image generating unit changes the resolution to the higher resolution by improving the resolution in vertical direction only, the resolution in the vertical direction being even in each partial area.