The present invention enables a geometric transformation matrix with a reference image that presents a planar region to be estimated with high accuracy even when correspondence with the reference image cannot be obtained. A first segment group extraction unit 120 extracts a segment, from within a segment group of an image, that corresponds to a direction parallel or perpendicular to a side of a rectangle included in the image from inside of the rectangle, said segment being extracted as a first segment group, and extracts a plurality of segments from the segment group that are different from the first segment group. From a plurality of segments derived by transforming the different plurality of segments using an affine transformation matrix, for which an angle with respect to an image reference direction of the first segment group is used as the angle of rotation, an edge point detection unit 150 extracts segments that correspond to the direction parallel or perpendicular to the side of the rectangle and detects four intersections of two segments selected from the extracted segments with image edges. A homography matrix estimation unit 160 calculates a geometric transformation matrix on the basis of the affine transformation matrix and a homography matrix calculated from the correspondence between the four intersections and four rectangle vertexes of a reference image.
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