1. A process control method for controlling a controlled object in such a manner that a deviation value of a controlled variable from a set point value is reduced, comprising steps of: predicting an output of the controlled object indicative of the controlled variable after a predetermined time has passed, assuming that an input of the controlled object indicative of a manipulating variable maintains a current value; inputting only a deviation between a predicted value of said controlled variable and said set point value to a fuzzy reasoning unit; and determining, based on the input deviation, a manipulating variable at a current time for the controlled object by fuzzy inference in said fuzzy reasoning unit; and using the manipulating variable to control the object.