PURPOSE: To prevent wrong fault judgement to output lowering of an inlet air amount sensor by detecting fault of the inlet air amount sensor by its output, and stopping detection of the fault until the output of the inlet air amount sensor becomes the predetermined level.

CONSTITUTION: An ECU 10 determined fuel injection amount based on respective signals from an AFS (inlet air amount sensor) 2, a crank angle sensor 11, starting switch 13, engine cooling water temperature switch 13 and a throttle sensor 4, and controls the pulse width of fuel injection pulse of an injection 9 by synchronizing with the signal from the crank angle sensor 11. And when all the burnoff conditions are established, the ECU 10 generates burnoff control signal 14. In this case, the fault is detected by the output level of the AFS 2. And after the burnoff control is finished, operation of the fault detecting unit is stopped until the output of the AFS sensor 2 reaches the predetermined level.