A plant control device includes a feedback controller that determines a control input of a plant, and a reference governor that corrects an initial target value and outputs the corrected initial target value to the feedback controller. The reference governor determines a target value satisfying an upper limit constraint to be a target value candidate that minimizes a value of an evaluation function. The reference governor determines the target value satisfying the upper limit constraint to be a value of the upper limit constraint when a value acquired by substituting, with the value of the upper limit constraint, a variable of a differential function acquired by differentiating the evaluation function with respect to the target value candidate is greater than or equal to zero.
