PURPOSE: To shorten the processing time by storing each information of coordinate lattice lines on the same line in a segment information table and performing the segment coupling processing.

CONSTITUTION: A data size setting means 24 recognizes an analysis area division number (m) in the X direction, and a processing frequency setting means 25 recognizes an analysis area division number (n) in the Y direction. A data read means 21 reads out data of a first segment based on the instruction of the data size setting means 24, and data of coordinate lattice lines in the X direction is stored in the first position of an analysis result data file 4, and data of first m-number of lines is read out and is stored in a segment information table 22. A segment coupling means 23 performs the segment coupling processing of coordinate lattice lines, and a data output means 27 outputs contents of the segment information table 22 to a CAD data base 5 when there are no segments to be coupled, and a processing frequency counting means 26 counts the frequency in processing. Thus, the processing speed is increased.