A highly reliable aerodynamic coefficient estimate can be computed, and computation of this aerodynamic coefficient estimate enables accurate detection of control surface failure/damage while reducing a discomfort for passengers. A deflection angle command signal generation means (5) generates a deflection angle command signal for estimating an aerodynamic coefficient indicating the aerodynamic characteristics of an airframe. A kinetic state quantity acquisition means (6) acquires a kinetic state quantity of the airframe that is obtained as a result of a control surface provided on the airframe being moved based on the deflection angle command signal. A candidate value calculation means (7) calculates candidate values for estimating the aerodynamic coefficient from the kinetic state quantity using two or more different estimations. An aerodynamic coefficient estimate determination means (8) determines an aerodynamic coefficient estimate based on the candidate values.