PURPOSE: To prevent a bearing combined in advance from falling into pieces and to facilitate bearing assembly by holding a paneling and a track wheel like a closed ring and friction-connecting the paneling with the track wheel in a hold part.

CONSTITUTION: A track groove ring 5 is arranged on a peripheral groove face 4 of a track wheel 6, and a rolling track 2 is formed in the track groove ring 5. The track wheel 6 made of plastic has a ring groove 12 in the peripheral direction for an open paneling 8 having a joint in the peripheral direction, and the paneling 8 is fitted in the ring groove 12 in the radial direction for the center 7 of a bearing. A joint of the paneling 8 is deviated in the peripheral direction for a joint of the track wheel 6 so that the paneling 8 and the track wheel 6 are mutually held like a closed ring by a force acting in the tangential direction. Consequently, since the paneling 8 and the track wheel 6 are friction- connected in the ring groove 12, return elasticity of the track wheel 6 which occurs slightly by the closed paneling 8 is absorbed, and the bearing does not fall into pieces.