A composite fire detector, comprising: a carbon monoxide detector configured to detect carbon monoxide; a smoke detector configured to detect smoke; a heat detector configured to detect heat; and a housing, a periphery of the housing being shaped like a circle, the housing comprising a base configured to be fixed to a ceiling member, and a cover which is disposed at a lower side of the base to cover the carbon monoxide detector, the smoke detector and the heat detector, characterized in that the base body is made from synthetic resin and shaped like a cylinder having a bottom; and the cover is made from synthetic resin, the cover comprising an upper cover which is shaped like a cylinder having a bottom, and a lower cover which is shaped like a cylinder having a bottom wall and protrudes downward from a peripheral part of an opening in center part of a bottom wall of the upper cover, the cover integrally comprising spacers which protrude upward from an upper edge of the upper cover so that a distance between a bottom wall of the base body and the upper edge becomes a prescribed distance, the spacers are arranged at regular intervals in a circumferential direction of the upper edge of the upper cover, each carbon monoxide inlet corresponds to a space surrounded by the upper edge of the upper cover, the bottom wall of the base body, and two spacers, adjoining in the peripheral direction of the housing, of the spacers, the housing is formed with carbon monoxide inlets arranged at regular intervals in a peripheral direction, at a first height position, of the housing, smoke inlets arranged at regular intervals in the peripheral direction, at a second height position lower than the first height position, of the housing, and heat inlets arranged at regular intervals in the peripheral direction, at a third height position lower than the second height position, of the housing, the carbon monoxide detector, the smoke detector and the heat detector are arranged at different heights in the housing, and the carbon monoxide detector is arranged between the carbon monoxide inlets and the smoke inlets. a carbon monoxide detector configured to detect carbon monoxide; a smoke detector configured to detect smoke; a heat detector configured to detect heat; and a housing, a periphery of the housing being shaped like a circle, the housing comprising a base configured to be fixed to a ceiling member, and a cover which is disposed at a lower side of the base to cover the carbon monoxide detector, the smoke detector and the heat detector, characterized in that the base body is made from synthetic resin and shaped like a cylinder having a bottom; and the cover is made from synthetic resin, the cover comprising an upper cover which is shaped like a cylinder having a bottom, and a lower cover which is shaped like a cylinder having a bottom wall and protrudes downward from a peripheral part of an opening in center part of a bottom wall of the upper cover, the cover integrally comprising spacers which protrude upward from an upper edge of the upper cover so that a distance between a bottom wall of the base body and the upper edge becomes a prescribed distance, the spacers are arranged at regular intervals in a circumferential direction of the upper edge of the upper cover, each carbon monoxide inlet corresponds to a space surrounded by the upper edge of the upper cover, the bottom wall of the base body, and two spacers, adjoining in the peripheral direction of the housing, of the spacers, the housing is formed with carbon monoxide inlets arranged at regular intervals in a peripheral direction, at a first height position, of the housing, smoke inlets arranged at regular intervals in the peripheral direction, at a second height position lower than the first height position, of the housing, and heat inlets arranged at regular intervals in the peripheral direction, at a third height position lower than the second height position, of the housing, the carbon monoxide detector, the smoke detector and the heat detector are arranged at different heights in the housing, and the carbon monoxide detector is arranged between the carbon monoxide inlets and the smoke inlets.