Disclosed is an apparatus and method for calculating a raw-cost necessary for combining images into one image by matching of stereo images. The raw-cost calculation apparatus includes an image acquirer, a window generator, a window mask generator, a window masker, and a raw-cost calculator. In the raw-cost calculation apparatus and method, a raw cost may be calculated by using an adaptive window mask so that accurate 3D information may be obtained on the boundary of thin structures even when stereo images are matched and combined.