PURPOSE: To prevent the development of faulty rupture positions by forming a rupture projection projected outward out of an estimated rupture and separation site of a bearing, making the estimated rupture and separation site higher in hardness than the other site with the aforesaid projection crushed down, and thereby applying load to the bearing in the direction of rupture and separation.
CONSTITUTION: A rupture and separation projection 7 is formed at the estimated rupture and separation site F of a bearing 2 in such a way as to be projected outward. Next, the estimated rupture and separation site F is made higher in hardness than the other site with the aforesaid projection 7 crushed down before the bearing 2 is processed for rupture and separation. Load is then applied to the bearing 2 in the direction of rupture and separation thereafter, so that the bearing 2 is ruptured so as to be separated. This constitution thereby enables the bearing 2 to be stably ruptured at the boundary of the estimated rupture and separation site F acting as a break starting point.