In an A/D conversion control apparatus for use in an electronic controller such as an engine ECU of a vehicle, each of successive sets of A/D converted values of an analog signal (each set comprising 3 or more values) is processed to obtain a median value of the set, and the median values are subjected to digital smoothing processing to obtain successive final result values, with effects of noise contained in the analog signal being effectively excluded. The final result values are suitable as control data, supplied to a control device such as a microcomputer of an ECU.