1. A stereo camera device detecting a distance to a subject, the stereo camera device comprising: two cameras that are installed and separated from each other by a base line length; and a calculation unit that calculates a distance to the subject on images based on the images acquired by the two cameras; wherein, the calculation unit includes an image processing unit, an offset value calculation unit, and a statistical processing unit, wherein the image processing unit is configured to search for corresponding points of the images acquired by the two cameras and calculate two parallaxes based on differences in positional coordinates of the corresponding points on the images, wherein the offset value calculation unit is configured to calculate parallax offset values across the images based on the two parallaxes calculated by the image processing unit at least at two time points, and wherein the statistical processing unit is configured to perform a statistical analysis on a distribution of the parallax offset values and determine an optimum value of the parallax offset values, the optimum value being used as a correction parameter.