As a technique of properly controlling an engine operation while preventing the knocking of the engine, a technique in which a knocking sensor is secured to the engine and an ignition timing control that controls an ignition timing on the basis of an output of the knocking sensor is performed has been known (see Patent Document 1).
This ignition timing control is a control that attempts to make full use of an engine output while preventing an occurrence of the knocking, by advancing the ignition timing step by step when the knocking is not detected by the knocking sensor, and by retarding the ignition timing when the knocking is detected.
The above ignition timing control using the output of the knocking sensor is commonly used for four-wheel vehicles. However, in a case of an engine whose structure is simple such as the general purpose engine for the small generator and the engine for the motorcycle, although an electronic controller that performs an engine control such as an engine revolution speed is used, the knocking sensor is not generally used. Thus, in the present circumstances, the ignition timing control to prevent the knocking is not carried out for such engine.