PURPOSE: To prevent a decrease in detection precision against temperature fluctuations and a change in the lapse of time by correcting the output signal of a negative suction pressure sensor by a value corresponding to atmospheric pressure.

CONSTITUTION: The negative suction pressure signal from the negative suction pressure sensor 14 is corrected by a negative suction pressure signal correcting circuit 17 into a signal corresponding accurately to negative suction pressure on the basis of the stored value of a correction value storage device 16. Then, a fuel injection valve 13 is controlled through an engine control circuit 18 on the basis of the accurate corrected negative suction pressure signal so that the optimum supply amount of fuel and the optimum ignition period corresponding to a load are secured. The stored value in the storage device 16 uses a negative suction pressure signal showing the atmospheric pressure when the atmospheric pressure is admitted to the negative suction pressure sensor 14.