PURPOSE: To describe and manage plural source programs having partially different processing by one source program without depending upon the function of a compiler.

CONSTITUTION: A different description part in a source program is divided by holding it between a comment line having a selection N start keyword and a comment line having a selection end keyword and a selection identification(ID) keyword for validating or invalidating the range is included in the comment line having the selection start keyword to unitarily manage the source program. A source program selecting device 1 acquires the selection ID keyword and stores the keyword in a selection specifying keyword storing table 12. A source I/O judging part 13 inputs the unitarily described source program 2 in each line, and when the comment line having the selection start keyword appears, judges that lines from the appearing comment line up to the comment line having the selection end keyword are invalid if a character string coincident with the selection ID keyword is not included in the appearing line, jumps these lines and outputs a source program 3 selected by judging other lines as valid lines.