An internal-combustion engine control system is able to suppress the occurrence of problems such as changes in air-fuel ratio. The internal-combustion engine control system is equipped with intake pressure detecting means for detecting intake pressure in the internal-combustion engine; operating state detecting means for detecting the operating state of the internal-combustion engine; and controlling means for controlling the operation of the internal-combustion engine according to the operating state of the internal-combustion engine; wherein the controlling means corrects the amount of the fuel injection according to a differential pressure between the intake pressure in a steady operation mode of the internal-combustion engine and an intake pressure detected by the intake pressure detecting means.