Improving stereo matching speed and accuracy, an image data input unit acquires image data of plural images of a predetermined region captured from plural different positions. A reference disparity setting unit sets a reference disparity suitable for the plural images. The search range setting unit sets a predetermined range smaller than the image range as a search range for stereo matching, by referring to points in the images between which the reference disparity set by the reference disparity setting unit is provided. A stereo matching unit searches out, for an arbitrary point in one of the plural images, a point in the other image that matches the arbitrary point, from the search range set by the search range setting unit, by referring to a point in the other image that provides the reference disparity set by the reference disparity setting unit.