A three-dimensional topographical data precision improving device (10) removing noise that occurs in water regions of three-dimensional topographical data comprises a water region specifying unit (13) specifying the range of any one water region; a feature extraction unit (14) extracting feature values within any one water region that describe altitude distribution pattern of each local region in the three-dimensional topographical data; a segmentation unit (15) segmenting the whole range into candidate water regions and non-water regions by comparing the feature values of the specified water region with those of each point in the three-dimensional topographical data; a water region extraction unit (16) extracting water regions from the candidate water regions; and a plane creation unit (17) creating a corrected plane of each water region using the altitudes of the surrounding non-water regions and replacing the water region extracted by the water region extraction unit (16) with the corrected plane.