A process control apparatus has a controller for performing a control operation including an integral operation for a set point signal supplied to a process and an output signal from the process and for generating a control signal to the process, and a reference model which has a desired transfer function of a control system and which receives the set point signal. The process control apparatus further has a first subtractor for subtracting the output signal of the reference model from the output signal of the process, an output error compensator for performing a control operation including an integral operation for the output error and for generating a compensation signal in such a manner that the output error becomes zero, and a second subtractor for subtracting the compensation signal from the output control signal of the controller.