A self-tuning controller apparatus which com­prises: a control response pattern recognition portion (4) for receiving a set-point (SV) and a controlled variable (PV) of a process and for obtaining three performance indexes from a controlled variable response pattern generated in response to a change in the set-­point or a disturbance; a control parameter correction portion (6) for qualitatively evaluating the three performance indexes and for inferring a correction value of a PID control parameter on the basis of the result of evaluation; and a control performance dissatisfaction degree evaluation portion (7) for evaluating the inferred correction value of the PID control parameter in accordance with the dissatisfaction degrees of the two performance indexes for the respective target speci­fications of the two of the three performance indexes. The control performance dissatisfaction degree evalua­tion portion acts to make the PID control parameter converge stably. In a process control system including a plurality of vertically distributed control elements each capable of self-tuning its control parameter, the control performance dissatisfaction degree evaluation portion contributes to autonomous functioning of each of the control elements.