To allow a simulation device to perform an operation close to the operation of a real machine and to evaluate a control program of a microcomputer in this environment.

When microcomputer development is evaluated and tested, the input terminal 2 and the output terminal 13 of a simulation device 1 are connected to a microcomputer 19. An input pattern discriminating part 3 discriminates whether or not a control signal from the microcomputer meets a prescribed condition. A counter control part 6 controls start, stop or count direction switching such as counting up and counting down about the operation of a counter according to the discriminated results. The counter counts up or counts down in a prescribed rate while the count operation is allowed. An output controlling part 9 outputs an output pattern corresponding to the count value of the counter from the output terminal to the microcomputer.