To provide information on optimum mixture injection timing and ignition timing for the combustion device of an engine based on the detected results by reducing a non-detection interval to accurately detect the position of a piston.

While a flywheel 10 is rotated, a detection sensor detects an index 20a formed on the inner surface of the flywheel 10 to accurately measure the speed of an engine and the position of the piston. Such an index 20a is substantially uniformly formed on a circumference with the same center as that of the flywheel 10 and divided into prescribed intervals to measure the rotational speed of the engine and accurately predict the position of the piston reaching the top dead center. Thus, a combustion device control system of the engine can be realized on the flywheel 10 without requiring a separate rotary disk, and the injection timing and the ignition timing of the mixture can be accurately controlled by the ECU of the engine.