PURPOSE: To prevent finning at the end face of a product, blow holding and deformation of the end face by fitting a piece and a block into the hole punched in a moving die in the axial center direction toward the end part of a cavity from a strap direction so that the gas in the cavity is released.

CONSTITUTION: The molten Al 15 charged into a sleeve 13 is advanced at a low speed by a plunger piston 14, and when the top of the metal 15 arrives at a gate 16, the metal is injected at a high speed. The metal 15 fills a space 17a for forming a short circuiting ring as shown by an arrow A and fills a space 17b for forming the short circuiting ring by passing the slit 18 of an iron core 1 for a revolving armature of a rotary electric machine. The air and gas forced to the end face on the strap 6 side in the space 17 during this time passes the slit 8 of a piece 7, is gathered in a hole 11 through the gas relief groove 10 of a block 9 and is released through a groove 12 into the atmosphere like an arrow G. The metal 15 does not leak in the slit 8 and the good product having no fin is obtd.