Abstract: A device for improving combustion efficiency of an internal combustion engine includes an elongated flexible sheet, a flexible metallic reflector attached to the flexible sheet for reflecting the extreme infra-red radiation, a ceramic radiation source attached to the reflector and a fastener for attaching the flexible sheet to an air intake duct of the engine with the radiation source facing toward the duct. The extreme infra-red radiation having a wavelength of from 8 .mu.m to 10 .mu.m irradiates the air incoming through the duct before combustion within the engine combustion chamber, whereby the combustion efficiency of the internal combustion engine is improved.