When a combustion feedback correction coefficient to which a predetermined value is added in correspondence to half miss firing judgment exceeds a heavy fuel judgment value (K0), heavy fuel judgment is made, and heavy fuel corresponding control for increasing the fuel amount by a combustion feedback correction coefficient (Kfb) and by prolongation of increasing fuel amount (τ) immediately after the startup is performed. When startup is consecutive startup, having a small drop width of a cooling water temperature (TH), from the last engine stop, and the number of times of ignition (Nig) accumulated during the last running is smaller than a warming judgment value (Nig0) at re-startup after running under the heavy fuel corresponding control, miss firing judgment is regarded as being impossible and alternative control for increasing the fuel amount is performed instead of the heavy fuel corresponding control.