It is an object of the present invention to provide a simulation tool, which can overcome complications of examinations by simulations as described above and can provide a designer with easy examinations. A simulation based on a design parameter of a unit is implemented. Furthermore, a simulation result implemented by the control device is output on a display screen as a graph. Then, the unit design parameter is corrected in accordance with a correction in the graph displayed on the display screen. Thus, the simulation can be retried easily.