PURPOSE: To secure a desired air-fuel ratio even at low temperatures and restrain an increase in emission of HC and CO by correcting, according to air density, an upper limiter of a basic fuel injection pulse width on the basis of a ratio of an intake air quantity of an internal combustion engine to an engine speed thereof.

CONSTITUTION: An air flow sensor 3 for detecting an intake air quantity is disposed on an intake side to an internal combustion engine 7 in an air cleaner 1. A crank angle sensor 16a for detecting an engine speed of the internal combustion engine 7 is provided in a distributor 16. A control unit 30 controls at least a fuel injection valve 13 on the basis of outputs from at least the sensors 3, 16a. The control unit 30 corrects, according to air density, an upper limiter of a basic fuel injection pulse calculated on the basis of a ratio of the intake air quantity to the engine speed. Consequently, it is possible to secure a desired air-fuel ratio even at low temperatures so as to enhance operating performance, and restrain an increase in emission of HC and CO.