The purpose of the present invention is to reduce calculation cost of plant evaluation. The plant evaluation device (5) is equipped with: a reception unit (51) for receiving an actual machine operation quantity during process control of a plant and an actual machine state quantity to be controlled by the process control; an estimation unit (52) for obtaining as an estimated state quantity, a state quantity obtained by substituting the actual machine operation quantity for the operation quantity in the process model by using a process model in which a mathematical relationship between an operation quantity and a state quantity during the process control is defined; and a comparison unit (53) for comparing the estimated state quantity with the actual machine state quantity.
