To provide a software coding system which improves the productivity of program development and which does not require maintenance.

An existing source file 4 is past software property and supplies a parts source code to a new program. Design document files 5a-5c have design information of the new program. In a source code generation part 7, an input control part 8, an output control part 9 and a parts control part 10 sequentially identify functions being the description units of the design document files 5a-5c, extract the corresponding parts file 12 in a temporary file 11 in a storage device, output generation source codes 14 as output information 13 in a recognized order in the design document files 5a-5c and generate the new program based on input information 1.