PURPOSE: To ensure the highly precise control of a control constant for a PID controller according to the desired target setting conditions by using a combinational control constant in response to the present control state value and at the same time by controlling the value of each control constant in response to the present control state value for operation of a manipulated variable in a control mode.

CONSTITUTION: A PID controller 1 inputs the deviation (e) between the target value (v) and a controlled variable (y) and operates a manipulated variable (u) against the deviation (e) to add the variable (u) to a controlled system 2. The system 2 adds the variable (y) varing according to the variable (u) to a control part 4. A differentiater 3 differentiates the deviation (e) and adds the differentiated value de/dt to a PID switching circuit 4. The circuit 4 operates the control state value (z) to show a control state based on the deviation (e) and the value de/dt. At the same time, the combinational value of PID control constants is previously set and used in a control mode. In the control mode, the combinational PID control constants corresponding to the present state (z) are set at each value and the variable (u) is operated.