1. A stereo image matching device comprising: a left camera and a right camera which take images of the same position at the same time to provide a stereo image; circuitry, comprising module configured to perform: a matching process based on a correlation for an image block on the basis of a disparity search range for each image block estimated and divided for the previous disparity image in two images provided from the left camera and the right camera, and outputs a disparity image for the current stereo image; and generating a disparity histogram configured with the number of pixels for each disparity value with respect to the disparity image output from the matching process, dividing the disparity image into multi-level blocks on the basis of the number of valid disparity values obtained by masking valid disparity values having the number of pixels equal to or more than a threshold value in the disparity histogram, estimating a disparity search range to include a valid disparity value for each divided image block, and providing the disparity search range; wherein the circuitry further comprises: a disparity histogram generating module which generates a disparity histogram configured with the number of pixels for each disparity with respect to an input image, a threshold value calculating module which calculates a threshold value to have a smaller value as the number of division times is increased for the image block, an image blocking module which masks valid disparity values equal to or more than the threshold value in the image block, divides the image block when the number of masked valid disparity values is equal to or more than a predetermined ratio of the maximum disparity search value, and performs a blocking process, and a disparity search range estimating module which estimates a disparity search range for each image block on the basis of pixel information corresponding to the valid disparity value for each image block divided in multi-level for one disparity image.