A failure determination device capable of performing failure determination for a shutter device of a vehicle with accuracy in a short time period. In an engine room of a vehicle, a condenser for a refrigeration cycle for an aircon is provided and at a front grille of the vehicle, a grille shutter device is provided for introducing ambient air for cooling the condenser into the engine room by opening a grille shutter. According to the failure determination device of the shutter device, a pressure of the refrigerant discharged from the condenser is detected as a refrigerant pressure. A failure of the grille shutter device is determined based on the refrigerant pressure, which changes at a large rate according to the opening/closing of the grille shutter, enabling failure determination with accuracy in a short time period.