1. A pose estimation system for performing object pose estimation by comparing an input image with a three-dimensional object model, the pose estimation system comprising: a pose candidate decision unit for generating at least one pose candidate; a comparison image generation unit for generating, according to the generated pose candidate, a plurality of comparison images similar to the input image, while projecting the three-dimensional object model to a two-dimensional image; a first sharpness extraction unit for extracting a first sharpness amount reflecting the sharpness from each of the plurality of comparison images; a weighted difference calculator for calculating a plurality of weighted differences by weighting the first sharpness amount to the difference between the input image and each of the comparison images; a determination unit for selecting a comparison image having the smallest weighted difference among the plurality of weighted differences and estimating an optimal pose based on the selected comparison image; and a second sharpness extraction unit for extracting a second sharpness amount reflecting the sharpness from the input image, wherein the weighted difference calculator calculates a plurality of weighted differences by weighting the difference between the second sharpness amount of the input image and the first sharpness amount of each of the comparison images to the difference between the input image and the comparison image, and wherein the first and second sharpness amounts are defined by a ratio of a number of pixels whose edge intensity is a threshold value or higher to the total number of pixels, a range of brightness values, dispersion of brightness values, or a number of characteristic points.