In order to provide a firewall that is capable of preventing flame passage through a through-hole without any sealant in a connecting part of a component in which a fastener through-hole is formed, a firewall 50 is provided which can prevent a flame from leaking out of the connecting part which connects a first member 51 to a second member 55, particularly through the fastener through-hole TH defined therein. In the firewall 50, the connecting part is a part of a fire-protection chamber 52. As sealing pieces 51d and 51e which also constitute a part of the fire-protection chamber 52 are in contact with each other, the flame is unable to enter into a closed space CA. Thus, the flame would not reach the connecting part, thereby preventing the flame from leaking out of the firewall 50 to the outside of a nacelle 23.