Abstract: A fire detector installed in a low ceiling surface of a vehicle such as an aircraft or train is equipped with an antitampering measure for preventing tampering such as covering the exposed portion of the fire detector with a paper cup or a vinyl bag or such as by sticking chewing gum or tissue paper in the smoke inlet portions thereof. Such tampering is usually carried out by passengers trying to sneak a smoke in a non-smoking area. The fire detector includes a main body having a head portion for letting in combustion products and a fire detection portion for performing fire detection on the basis of the combustion products let in from the head portion, and a mounting portion containing most of the main body and provided with a central opening portion for allowing the head portion to protrude from the ceiling surface so as to perform fire monitoring.