1. An apparatus for generating depth information comprising: an image downsizer configured to downsize an input stereo image by a predetermined magnification to generate a downsized stereo image; a rawcost calculator configured to calculate rawcosts for the downsized stereo image; a mapper configured to map the rawcosts to the input stereo image; an interpolator configured to perform interpolation and cost aggregation for the rawcosts; and a depth information generator configured to calculate an optimal disparity for each pixel of the input stereo image by referring to the rawcosts and generate depth information corresponding to the optimal disparity.