A roller retainer mounted on a roller comprises a first guiding frame and a second guiding frame that are integrally connected with each other in a vertically staggered manner. The first guiding frame and the second guiding frame are located along the two diagonals of the roller respectively. The thickness of the first guiding frame and the second guiding frame is utilized to keep the space between the two non-loading surfaces of roller and a track. The roller retainer can further keep the space between each roller. Thereby, the roller retainer can prevent the rollers from contacting each other; the loading surfaces can still contact the track and the non-loading surfaces are prevented from colliding with and rubbing against the track, thus reducing the noise and ensuring the moving direction.