PURPOSE: To surely prevent an engine from recklessly running, by providing an idling switch, an intermediate switch and a full-open swtich in an accelerator position sensor, and as well by providing a computer for controlling an injector.

CONSTITUTION: An idling switch 10, an intermediate switch 11 and a full-open switch 12 are provided in an accelerator position sensor 9. A computer 13 judges a desirable running condition in accordance with the combination of ON and OFF signals from the switches 10 through 12 when the accelerator position sensor 9 fails, and controls an injector 6, accordingly. With this arrangement, when the accelerator position sensor fails, the reckless running of the engine is surely prevented, and as well the running to some degree may be made.