To enlarge an application range as a heating furnace by uniformly emitting a far infrared energy as much as possible even in a protrusion and recess shape or a complicated shape on a surface of a material to be treated.

In the far infrared heater furnace comprising many far infrared heaters 40a, 41a, 41b, 42a, 42b, 43a,..., mounted at fitments 31, 32,... and arranged on an inner wall surface of a furnace body to heat materials 21, 22 to be heated and disposed therein, many sets are arranged along the wall surface like a combination of the same constitution as that of a pair of far infrared ray heaters 41b, 41a disposed in the state that a main emitting axis 51b of the heater 41b is intersected with a main emitting axis 52a of the heater 42a such as, for example, a combination of the heaters 40b, 41a, 42b and 43a.