It is an object to improve the accuracy of a house change judgment based on images and the like acquired by an airplane. A terrain altitude is subtracted from an attitude value of a digital surface model (DSM) acquired from an airplane or the like to generate a normalized DSM (NDSM). A judgment target region is segmented into a plurality of regions of elevated part for each elevated part with a size corresponding to a house appearing on the NDSM. An outline of the house is extracted from each region of elevated part and a house object containing three-dimensional information on the house is defined by the outline and NDSM data within the outline. The house objects acquired at two different time points, respectively, are compared to detect a variation between the two different time points, and a judgment as to a house change is made based on the variation.