To provide a continuous furnace not requiring wide installing space, not necessary of the returning system of base plates, enabling to stabilize the oxygen density of atmosphere at low level and saving the quantity of injecting inert gas to little quantity.

A furnace body 1 is annular and the carrying in gate 9 and the carrying out gate 10 of the base plates are arranged to the same position of it. The base plate 8 mounted with objects to be calcinated are carried into the inside of the furnace 3 through the carrying in gate 9 and calcinated during a circulation of it by a rotating body 4 inside the annular furnace. The calcination can be performed by putting on box shape muffles on the base plates 8 and supplying the atmosphere gas into the inside of the box shape muffles.