Abstract: A furnace of decreasing oxygen concentration to ultra low amount is basically characterized by providing a furnace body divided into a plurality of zones, a device for supplying a non-oxidizing or a reducing atmospheric gas into each of the zones so as to increase the internal pressure, shutter devices provided at least at an inlet and an outlet of the furnace body for checking the flowing atmosphere, transferring devices installed at the inside of the furnace, at the interior and at the outside thereof respectively, and a control device for opening the shutter device before the work in a transferring direction, wherein the transferring device installed within the furnace supports the work at its both sides of the under surface and continuously send it while the upper surface of the work is exposed to the atmosphere in the furnace.