The present invention provides an aircraft safety device which can reliably prevent explosion of a fuel tank even if an inflammable gas is ignited. A safety device for explosion-proofing a fuel tank which stores fuel of an aircraft includes: a flame propagation blocking part which blocks propagation of a flame from the outside to the inside of the fuel tank through a ventilation passage which allows ventilation between the inside and the outside of the fuel tank; and a gas supply suppressing part which, when heated by the heat of the flame, suppresses supply of an inflammable gas containing the fuel gas to the flame through the ventilation passage.