There is provided a safety device for aircraft, that prevents an explosion of a fuel tank storing aviation fuel, the safety device including: a flame arrester that is arranged near an end of a ventilation passage on an aircraft outer side, as a part of the ventilation passage allowing the inside of the fuel tank and an outside of the aircraft to communicate with each other, to prevent a flame propagation into the fuel tank from the outside of the aircraft through the ventilation passage; and a heat transfer reducing part that is arranged closer to the outside of the aircraft than the flame arrester to prevent heat transfer to the fuel in the fuel tank from the flame.