PURPOSE: To reduce the production cost of a product by omitting machining after forming.

CONSTITUTION: In the condition of opening dies by separating a movable die 3 from a fixed die 2, the hole 10 in the product 9 is exposed to the outside air and cooled and shrunk, but just after opening the dies, since a core pin 5 is already drawn out from the hole 10, the inner peripheral surface 10a of the hole 10 is opened by separating from the core pin 5. Then, even if the inner diameter of the inner peripheral surface 10a becomes small caused by the cooling and the shrinkage, the galling and the burning easily developed on the inner peripheral surface 10a at the time of drawing out the core pin 5 are eliminated. Since a draft of the core pin 5 is made to be 0°00' to about 0°20', the inner peripheral surface 10a of the hole 10 is formed so as to match to this draft, a fit tolerance having high precision is obtd. In order to further surely prevent the galling and the burning, the surrounding temp. of a cavity and the surface temp. of the core pin 5 in the dies 1 are controlled by utilizing a fluid passage 8 for adjusting the temp.