PURPOSE: To provide a process signal control system by which a complicated data processing and control can be executed with superior reliability and which can be realized by inexpensive device constitution.

CONSTITUTION: In a digital type control mechanism where a controller 1 which controls/operates a process signal and a personal computer 2 are combined, a control operation is executed by using an input signal (deviation signal) gone back from present to prescribed sampling time. Two groups for the proportional coefficients of respective signals are prepared. A prescribed value is previously given to one coefficient group. The other coefficient group is corrected by operating the coefficient at every sampling time in accordance with an algorithm which is previously given by using the personal computer. Usually, the product sum of the corrected coefficient and the input signal is set to be a control signal. When abnormality occurs in the personal computer, it is identified and it is substituted for the prescribed value which is previously inputted. A production sum is operated and the control signal is made.