PURPOSE: To realize a fuzzy control method based on the past observation data on the control subjects including the operation history of an operator, etc.

CONSTITUTION: The observation data stored in a data storage part 8 are converted into a feature vector form, and a small number of feature vectors are sorted into plural clusters by clustering. The center value of each cluster is stored in a cluster center value storage part 1. In an actual fuzzy control mode, a membership function computing part 3 calculates the distribution of sureness as a membership function for each cluster based on the cluster center value stored in the part 1, the present observation value of a controlled system 2, the target controlled variable, and the target arriving time. These calculated membership functions are synthesized. Then a non-fuzzy computing part 4 decides the manipulated variable to be outputted to the system 2 based on the synthetic membership function. The decided manipulated variable is outputted to the system 2.