A servo controller includes: a reference model unit which inputs a reference to generate a model output and a model input; a feedback control unit which generates a feedback input so that a control output of a plant follows the model output; and an adder which adds the model input and the feedback input, in which the reference model unit includes: a mathematical model which simulates characteristics of the plant, and generates the model output and a state variable from the model input; a model input memory which outputs a past model input; a model controller which inputs the reference, the state variable, and the past model input to generate the model input; and a model controller determining unit which determines the model controller based on the reference, the state variable, and the past model input.