To provide a heater furnace having a large length of soaking and being excellent in thermal efficiency and further in cooling efficiency.

This heater furnace comprises core tubes 1 and 2 holding an object of heating inside, heaters 7 and 8 enabling impression of heat on the core tubes 1 and 2 from the outer peripheries thereof, heat insulating materials 4 and 5 provided outside the heaters 1 and 8 and a cooling part 10 for cooling the heat insulating materials 4 and 5. In this case, the heater is divided into the sub-heater 7 and the main heater 8 and the sectional shape of the main heater 8 is made nonuniform.