Preventing incomplete combustion of fuel in a heat apparatus and equipment. Radioactive substance 4 is fixed to a sheet-like material 3 and this sheet-like material is attached to an air supply path A or a fuel supply path F of heat apparatus or equipment. Alternatively, radioactive substance 4 is mixed in raw material resin 7 and part of the air supply path A or the fuel supply path F is formed with an obtained compound. Or radioactive substance 4 is mixed in a paint 8 and this paint is applied to the air supply path A or the fuel supply path F. Consequently, air or fuel supplied to the heat apparatus or heat equipment is excited by radioactive ray so as to intensify chemical reaction activity of air or fuel thereby promoting oxidation reaction of oxygen namely combustion and preventing incomplete combustion.