A simulation device including a simulation computer is used to simulate peripheral equipment of a real-time system having two stored program computers operating on a load-sharing basis to check and contribute to the development of the two-computer system program. The simulation device includes a time control arrangement containing counters cooperatively arranged with respect to each other and the three computers to check and develop a normally continuously running program by a simulating process which operates in a step-by-step manner and yet maintains the real-time and duration concepts when simulated peripheral equipment is involved in the simulation process and when any time consuming process is simulated.