NOVELTY - A heat-resistant resin film generates 0.01-4 mu g/cm2 of outgas when heated in a bottom of helium airflow at 450 degrees C for 30 minutes.    USE - Heat-resistant resin film is used for manufacturing image display apparatus e.g. organic electroluminescent display (all claimed). Can also be used for planarizing film of thin-film transistor substrate, insulating layer of organic transistor, flexible printed circuit board, surface-protection film and interlayer insulation film of semiconductor element, and substrate for flexible display, flexible electronic paper, flexible solar cell and flexible color filter.    ADVANTAGE - The heat-resistant resin film has excellent mechanical characteristics and outgas characteristics.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) manufacture of heat-resistant resin film, which involves coating a solution containing precursor of heat-resistant resin on a support component, and heating in atmosphere with 10 vol.% or more oxygen at temperature (t1) of more than 200 degrees C, and then in atmosphere with 3 vol.% or less at temperature (t2) of more than the temperature (t1);    (2) heating furnace (10), which has a temperature measurement portion (22) for measuring temperature in a furnace (11), a temperature control portion (21) for adjusting temperature in the furnace, an oxygen concentration measurement portion for measuring oxygen concentration in the furnace, a gas flow rate adjustment portion for adjusting flow volume of heating atmospheric gas into the furnace, and a control portion (71) for controlling the temperature control portion and gas flow rate adjustment portion. The control portion controls the gas flow rate adjustment portion based on oxygen concentration in the furnace measured in the oxygen concentration measurement portion. After the oxygen concentration reaches predetermined oxygen concentration, the temperature control portion is controlled such that temperature in the furnace measured in the temperature measurement portion turns into predetermined temperature; and    (3) manufacture of image display apparatus, which involves manufacturing the heat-resistant resin film, and forming a pixel drive element or color pixel on the heat-resistant resin film.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of heating furnace.    Heating furnace (10)    Furnace (11)    Temperature control portion (21)    Temperature measurement portion (22)    Control portion (71)