PURPOSE: To make simulation results and circuit diagrams correspond to each other instantaneously and to obtain the results of all signal lines of a circuit line at a time by simulating pieces of information on respective parts of the circuit line by a computer and combining the results with the circuit diagrams.

CONSTITUTION: Pieces of information from storage devices 1 and 2 stored with circuit diagram information and input information of simulation are inputted to the computer 3 to perform simulation. A storage device 4 for output information is stored with the simulation results of all the signal line of the circuit diagrams. Further, the circuit diagram information from the device 1 and the simulation result from the device 4 are combined by a display controller 5 to display the circuit diagram and simulation results on a graphic display 6 at a time.