PURPOSE: To properly conduct a feedback control in accordance with the volatility of a fuel by detecting the fuel property related to the volatility of the fuel, and correcting, when the volatility is poor, the control range of the feedback control to allow the transfer in the direction improving the combustive state against the time with a good volatility.

CONSTITUTION: An ignition plug 17 is disposed facing the combustion chamber 3 of an engine body 1, and a discharged voltage is sent to the ignition plug 17 through an ignition coil 18 and a distributor 19 to regulate the ignition timing. An ignition signal is outputted from a controller 20 to the ignition coil 18, and a combustion control means for regulating the combustive state of the engine by this regulation of the ignition timing is constituted. In this case, in the controller 20, a signal related to the volatility of the fuel is detected and judged from the fluctuation of engine rotating speed at the time of engine start. When it is detected that the fuel having a low volatility is supplied, the control range of feedback control is changed and corrected relative to the time with good volatility to allow the transfer in the direction improving the combustive state.