To easily set a specification by a method wherein a simulation program is developed based on the types and names of a compressor and a heat exchanger and the simulation program is executed to do a simulation arithmetic based on the specifications and characteristics arithmetic formulas of the compressor and the heat exchanger.

A pre-processor 5 selects necessary sub-programs from a sub-program group 9 according to data such as connection relations between a compressor and a heat exchanger, types and names, etc., that are input by a key board 2, and produces a generator 6 that links those sub-programs. The generator 6 created is executed to produce a main processor 7, i.e., a simulation program. The main processor 7 produced reads out specification data on components from a data base file 3 to perform a simulation arithmetic, stores the results of the simulation arithmetic in an output file 10 and indicates them on a display 1 graphically.