PURPOSE: To make compact the structure of an infrared-ray combusting apparatus for combusting gas fuel, by employing a diffuse combustion system in which combusting air is introduced from air inlet ports and supplied to round holes formed in a combustion casing, and thereby making it unnecessary to provide a special mixing pipe.

CONSTITUTION: Gas fuel carried through a gas supply pipe 4 is issued into a combustion casing 1 from many gas injection ports 10. When the gas fuel is subsequently ignited by an igniting means (not shown), large flame is formed and combustion is started by air introduced from a plurality of round holes 2 formed in both side faces of the combustion casing 1, so that casing 1 begins to be red-heated. High-temperature gas produced by combustion flows upward along the wall surfaces of casing 1 while heating the same, and then discharged to the outside from an upper exhaust port. Air in a room is heated by the exhaust gas. At the same time, infrared rays are radiated through a heat transmitting member 8 attached to an outer casing 5 which is disposed with proper spacing from the front and rear surfaces of combustion casing 1, so that the room can be heated more effectively.