PURPOSE: To perform debug even without a controlled device, to confirm a software operation when abnormality occurs in hardware, and to perform both maintenance of software after shipping and the confirmation of an operation after improvement by providing a program which simulates the operation of the hardware of the controlled device.

CONSTITUTION: When the computer 4 for control of a controller 10 outputs an instruction to the controlled device, a state signal is returned by operating the hardware. The computer 4 for control judges the state signal, and outputs the next instruction signal. Since the hardware can be operated in constant sequence in such way, the simulation of such operation is performed by the program 11, and signal input/output to a control signal output part 5 and a state signal input part 6 is performed by the RAM 12 of a debug computer 14. Also, when it is assumed that the abnormality occurs in the controlled device by a personal computer 15, the computer 4 for control of the controller 10 confirms the operation when the abnormality occurs in the hardware.