The present invention provides an annular roller device for a sliding window/door, which is proposed as a roller device having a new structure wherein the roller device installed under a door sash can move a sliding window/door having heavy weight, and can maximize the open glass portion of the window/door by minimizing the height of the space required to install the roller device, thereby providing a more open view. The roller device has a structure in which, even when a rail installed on a window frame is not horizontal or the bottom portion of a window is not completely flat, all multiple rolling members, which constitute a ring-shaped rolling unit wound around a load-bearing plate (1220) comprising segment bodies (1221, 1222) rotatably connected to each other by a pivot pin (1225) extending therethrough, form contact points with the rail or the bottom portion, and thus each of the rolling members is prevented from being loaded with excessive weight.