PURPOSE: To provide proper air-fuel ratio by calculating a basic fuel injection amount, comparing a change amount of intake pipe pressure with a preset upper limit value to determine the change amount and calculating a fuel injec tion correction amount based on the obtained correction pressure change amount added to or subtracted from the basic fuel injection amount.

CONSTITUTION: Volumetric efficiency is calculated from outputs of an intake pipe pressure sensor 101 and a crank angle sensor 102, and a basic fuel injection amount is calculated in a basic fuel injection amount calculating means 104. On the other hand, an output of an intake pipe pressure change amount calculating means 105 is compared with a preset intake pipe pressure upper limit value in an upper limit value setting means 106, to determine a change amount with the upper limit value serving as the limit. A correction pressure change amount is obtained from this determined change amount and a pressure change amount correction coefficient based on an output of a throttle position sensor 108, and a fuel injection correction amount is calculated in a fuel correction amount calculating means 112 and added to or subtracted from the basic fuel injection amount. Thus by operation with proper air-fuel ratio, drivability is improved.