A method for producing a ring core having a plurality of separate core plates with lobes defined on an inner circumferential surface thereof, the separate core plates being arranged and stacked in a ring-shaped pattern. The method includes the steps of supporting the separate core plates with either one of an inner guide member being disposed radially inwardly of the separate core plates stacked in the ring-shaped pattern and an outer guide member disposed radially outwardly of the separate core plates, and applying a pressure from the other of the inner guide member and the outer guide member, wherein the inner guide member has recesses corresponding to the lobes for positioning and supporting the lobes, and stacking the separate core plates in the ring-shaped pattern to form the ring core, while rotating the separate core plates in unison through a predetermined angle with the inner and outer guide members.