The invention relates to a support disk for supporting a rotor used in an open-end spinning machine comprising a bearing ring and a supporting ring attached to the outer periphery of the bearing ring and made of a polymer material having elasticity. The bearing ring has a side ring at least one side in the sides of the outer edge, and the side ring is arranged at an interval and connected to the bearing ring through a supporting part. The bearing ring and the side ring have the same supporting ring on each outer periphery.