PURPOSE: To enable effective sealing under high temperatures by using a thermoplastic polymer containing material to be cross-linked under the influence of radiation as a seal material.

CONSTITUTION: A seal performs ionization radiation by using thermoplastic copolymer containing material capable of being cross-linked by radiation and adjusts the radiation strength in order to cross-link different seals at the different degrees. In injection molding of the seals, sealing parts 1 of the seal and a shape holding part 2 are formed in the different stages, respective parts are made of different materials, and the elastic parts 1 are securely connected to the shape holding part 2 by cross-linking. The shape holding part 2 is formed harder than the elastic part 1 by high-degree cross-linking. The seal formed in this way maintains its shape while being used in a rolling bearing at near or above the melting point of the thermoplastic polymer.