To detect breakage between patches from ridge line data by preparing the ridge line data combining the respective patches from patch data expressing a three-dimensional shape by plural patches.

This method and device for detecting breakage between patches prepares ridge line data from patch data stored in a patch data storing part 11 by means of a processing part 10 to store the ridge line data in a ridge line data storing part 12. The part 10 judges whether a ridge line belonging to only one opposed patch exists within the ridge line data. When a ridge line belonging to only one opposed patch exists within the ridge line data as the result of the judgement, an information part 13 gives information that breakage between he patches exists in the patch data.