A throttle full-closure detecting apparatus for judging the full-closure state of a throttle valve uses the minimum value of a throttle sensor voltage so that the apparatus output is compensated for, in particular, a change in temperature. In a timer routine in the apparatus, first, the throttle sensor output is AD-converted and the thus AD-converted output is stored into a RAM and a general purpose register Ar. Next, a full-closure angle is stored in a compare register Cr and the contents of Ar and Cr are compared with each other so that when Cr>Ar, the AD-converted throttle value is stored as a full-closure angle and first storage updating is performed with the minimum throttle opening as the angle. Further, second updating for adding a specified value to the stored value of the full-closure angle is performed at a period sufficiently larger than the period of the time routine, and the first updating is made ready after the second updating.