PURPOSE: To improve the productivity of a titled jig by constituting the jig of plural pieces of water soluble unit rings and forming inside and outside end faces and circular conical faces to each unit ring.

CONSTITUTION: The unit ring is formed by binding the molding grains consisting of high alumina sand, etc. as aggregate and added with barium carbonate and potassium carbonate by a binder such as water glass so that the shape thereof is collapsed by water. The unit has the inside annular end faces 1a, 1b and outside annular end faces 1e, 1f at both ends and is formed with the circular conical faces 1c, 1d rising in the same direction. Steel plates are laminated to a mandrel 65 and thereafter the rings 1 are fitted by each piece to the outside circumference of the iron core 7 and the end faces are superposed on each other. After a cage type conductor 10 is cast, molds 8, 9 are removed and water is added thereto to collapse the rings 1 and the spacers 2. Since the jig can be formed to a desired axial size by increasing or decreasing the number of the rings 1 according to the above-mentioned method, the productivity is improved.