PURPOSE: To enable the formation of a rotor iron core of any thickness when the outside diameter of the rotor iron core is the same and to prevent the generation of fins, by forming conductors and end rings while the rotor iron core is held in place under pressure between the 1st and the 2nd molds.

CONSTITUTION: A rotor iron core 5 is inserted to the inside of a guide 14, and is placed on a bottom mold 4. Forming molds 1 are thereafter clamped and a top mold 2 descends until it comes into tight contact with the top surface of a middle mold 3. On the other hand, a bottom mold 4 ascends and a curved plate 15 enters the inside of a deep groove 13 until it contacts the bottom surface of the mold 3. Then, the core 5 receives the pressing force of a hydraulic cylinder or the like which is a driving source for moving the same upward. The core is thus strongly held in place under pressure between the mold 3 and the mold 4. The melt of Al in this state is forcibly fed into a cavity 7 through a runner 9 and a sprue 10; further, the molten metal is forcibly fed into a cavity 12 through the closed slot 5a of the core 5. Thereafter, the molten metal is cooled to solidify, whereby conductors 18 and end rings 6, 11 are formed.