Provided is a complex sintering furnace to sequentially perform a bake-out process and a sintering process for molding ceramic products. The complex sintering furnace includes: a support frame; a pair of furnace bodies supported on the top of the support frame and having a built-in heat insulator covered by a disc-shaped cover; a pair of rails arranged under the support frame in parallel in a length direction along arrangement of the furnace bodies; a rotating base horizontally transferred along the rails and rotatably connected to bottoms of the furnace bodies when the rotating base is vertically transferred directly under the bottoms of the furnace bodies, the rotating base including a separately rotating setter mounted the top thereof; and an ascending/descending apparatus mounted under the rotating bases and having a ball-screw type rotation shaft to vertically ascend/descend the rotating base at the same time of the separate rotation of the setters. Accordingly, the production efficiency of the ceramic products can be significantly improved by rapidly transferring to the post-processes and simultaneously performing the bake-out process and the sintering process.