PURPOSE: To simplify mechanism by constituting a cooling fan starter in such a manner that a gas introducing port for introducing a refrigerant gas is provided in the rotating direction of a cooling fan so as to face the cooling fan.

CONSTITUTION: A vacuum gas hardening furnace is set with a treating material A in a treatment chamber 2 and the inside of the furnace is evacuated to a vacuum through a discharge pipe 10. After the treating material is heated to the prescribed hardening temp. by a heater 5 for heating, the refrigerant gas is introduced through the furnace into the gas introducing pipe 11 and is circulated by the cooling fan 3 in the furnace by which the treating material A is quickly cooled. The top ends 11a, 11b of the gas introducing pipe 11 for introducing the refrigerant gas into the furnace are provided in the rotating direction of the cooling fan 3 so as to face the cooling fan 3. A motor 7 is turned on to run after the cooling fan 3 is started by the refrigerant gas.