To enhance uniform heating performance by averaging the heat being radiated from a heater toward an object to be sintered thereby bringing the temperature of gas as close as the sintering temperature when the gas arrives on the object to be sintered.

The inner heating sintering furnace comprises a sintering space for receiving an object to be sintered at the central part in a furnace body 10, a heater 18 disposed on the side of the sintering space, and a reflector 20 surrounding the sintering space including the heater. A partition panel 26 is provided between the heater and the object to be sintered in order to average the heat being radiated from the heater toward the object to be sintered. Piping 30 for supplying gas into the furnace body is arranged at the lower part between the heater and the partition panel. The gas is preheated in the piping and discharged upward between the heater and the partition panel and then supplied into the sintering space through a gap at the upper part of the partition panel.