PURPOSE: To provide the economical controller which evades the complexity of a program and changes optionally a control constant from outside, and can speedily and securely be designed, manufactured, and adjusted.

CONSTITUTION: The controller which performs control arithmetic by a digital computer on the basis of the measurement results of the states of a controlled system by properly arranged sensors to calculate a necessary manipulated variable, and outputs a command signal to a manipulator is so constituted that the control constant, etc., can be set as an input value and varied with external inputs 9 and 10 during real-time control.