PURPOSE: To sensitively detect abnormality, and at the same time, even if there is a noise of the same phase and same level, to enable the detection thereof by converting a mechanical control input into a plurality of electric signals of differnt conversion ratios, and further by enlarging once again the amount of abnormality for comparison.

CONSTITUTION: In an accelerator operation system of an automobile, a pair of converters for generating two kinds of analogue electric signals in accordance with the turning angle of a shaft 2a are incorporated in an accelerator opening sensor 2, while the conversion ratios of the respective converters are different to each other. The two analogue electric signals are sent to an engine control computer 5 through transmission cables 4a, 4b. In this way, one mechanical control input is converted into a plurality of electric signals of different patterns in accordance with the amount of control input, and a comparison/calculating part reads the converted electric signals and calculates the amount of control input, and on the basis of the difference in the calculated results, the presence of abnormality is judged. Thus, the abnormality of a control input signal transmission system can be sensitively detected.