A control device includes a target value acquisition portion configured to acquire a target value of amount of control per predetermined computation cycle, a control portion configured to control the control target using the acquired target value, a target smoothing value calculation portion configured to calculate a target smoothing value in which a temporal change in the target value is slowed down, and a state determination portion configured to calculate a first difference that is a difference between the target value and the target smoothing value to determine that the amount of control is in a transient state when the calculated first difference is equal to or more than a predetermined first threshold value and to determine that the amount of control is in a non-transient state when the first difference is smaller than the first threshold value.