To provide a thermal treatment device which does not require a loading area or a lift mechanism below a processing vessel, can be reduced in height, made simple in structure, and improved in processing.

A holder 1 holds works W disposed at a prescribed interval in a vertical direction and is housed in a processing vessel 3 to process the works W as prescribed, an opening 9 is provided to the side wall of the processing chamber 3 to load or unload the holder 1 into or from the chamber 3, an openable lid 10 is provided to hermetically stop up the opening 9, a gas inlet 4 and a gas exhaust vent 5 are provided to the processing vessel 3, and heaters 15 and 16 of resistance heating elements are provided around the processing vessel 3 and inside the lid 10 to heat the works W inside the processing vessel.