PURPOSE: To maintain the air-fuel ratio at a preset value under a high load while running on a highland by decreasing the maximum fuel injection quantity when a throttle valve is fully opened during the travel on the highland.

CONSTITUTION: A control device 68 reads out the value data of the maximum fuel injection quantity corresponding to the output of a rotation angle sensor 58 from an ROM 74. Next, the product of the correction value determined by the first highland compensation level and the maximum fuel injection quantity is calculated. This value becomes the maximum fuel injection quantity when a throttle valve is fully opened during the travel on the highland. Furthermore, a fuel injection pulse width is compared with the maximum fuel injection pulse width during the travel on the highland, and if the former is larger than the latter, the former is limited to the value of the latter. Thereby, the air-fuel ratio under a high load while running on the highland can be maintained at a preset value.