PURPOSE: To obtain a device for heat treatment which is capable of degreasing a ceramic of AlN simultaneously with its firing.

CONSTITUTION: A device for heat treatment for moldings of AlN, of which either the heater 2 or the heat-insulating material 3 is of carbon, is provided with a muffle 1 of which at least the inner side consists of a material other than carbon (AlN, BN, Si3N4, W, Mo, etc.) and which is positioned on the inner side of both the heater 2 and the heat-insulating material 3 and fixed inside the furnace. The muffle 1 is provided with an intake pipe 7 for nitrogen and a gas-discharge pipe 8 for removing the gas produced at the time of the degreasing from the furnace to the outside.