ARITHMETIC UNIT AND PARALLAX CALCULATION METHOD

An operation device includes: a first disparity search unit that uses a standard image that is an image obtained by capturing with a first camera and a reference image that is an image obtained by capturing with a second camera to calculate a disparity in the standard image in a unit of a first block and generate a temporary distance image; a disparity invalidity determination unit that identifies an invalid region for which disparity calculation from the temporary distance image has failed; a condition generation unit that generates a search condition including disparity candidates of the invalid region using the temporary distance image; and a second disparity search unit that uses the standard image, the reference image, and the search condition to calculate a disparity of the invalid region in a unit of a second block having a size equal to or smaller than a size of the first block.