A simulation system for an automotive internal combustion engine includes a low inertia power generator which includes a direct current motor and a speed increasing device. An engine characteristic generator derives a first signal indicative of a first output torque to be derived as an output of the low inertia power generator. The first output torque is equivalent to that of the engine. A first compensation torque is derived for compensation in view of a set engine inertia. A second compensation torque is further derived for compensation in view of a set inertia of the low inertia power generator. A third compensation torque is further derived based on the first and second compensation torques for compensating a differential in inertia between the engine and the low inertia power generator. A control signal is derived based on the first signal and the third compensation torque. The control signal is fed to the low inertia power generator for controlling operation of the direct current motor so as to provide a second output torque as the output of the low inertia power generator. The second output torque is equivalent to the first output torque. Accordingly, an output characteristic equivalent to that of the engine is provided as the output of the low inertia power generator.