1. An image processing device, to which pixel signals of a plurality of adjacent pixels are simultaneously input, configured to simultaneously find correlations between a plurality of target pixels adjacent to each other and corresponding reference pixels with pixels around the plurality of target pixels for each of the plurality of target pixels, the image processing device comprising: an extended region sum of absolute differences (SAD) calculation unit configured to define each of an extended target region obtained by combining a plurality of target regions predetermined for each of the plurality of target pixels adjacent to each other to be simultaneously correlated and an extended reference region, which corresponds to the extended target region, obtained by combining a plurality of reference regions predetermined for each of reference pixels corresponding to the plurality of target pixels, the extended region SAD calculation unit being configured to output an extended SAD calculation result obtained by performing SAD calculations based on values represented by pixel signals of pixels included in the defined extended target region and the defined extended reference region; and subtraction processing units equal in number to the target pixels adjacent to each other to be simultaneously correlated, the subtraction processing units being configured to correspond to the plurality of target pixels and to output SAD calculation results obtained by performing subtraction processes based on the extended SAD calculation result and an SAD calculation result corresponding to a region of a peripheral pixel which is not included in a predetermined target region for the plurality of target pixels to which the subtraction processing units correspond.