Abstract: A manipulated variable to be applied to a process and a process variable, are gathered by data gathering apparatus. In a modeling apparatus, which includes a process model, internal parameters thereof are adjusted so that an output of the process model may match the process variable. Accuracy of the process model is calculated by an estimation accuracy operating apparatus. The modeling apparatus is started when the manipulated variable or process variable changes to become larger than a fixed value, and control constants are derived from the outputs of the modeling apparatus and the estimation accuracy operating apparatus. The gain constant of the process model is determined by the output of the process model and the process variable.