A linear motion guide unit is disclosed, in which components required for a slider are all joined together with no fasteners including bolts, screws, and so on used conventional assembly operations, but mutual fit-engagement of any components with their mating counterparts. This allows reducing the number of components to cope with a modern tendency of miniaturization of the linear motion guide system. The slider includes a carriage casing composed of end panels facing forward and aft ends of a carriage, one to each end, and side panels facing widthwise opposing sides of the carriage, one to each, the end and side panels being connected integrally to surround the carriage. To complete the slider, the carriage first fits between the end panels of the carriage casing. Then, end caps are applied to outward surfaces of the end panels of the carriage casing and joined together by making fit-engagement of mating parts on the end caps with counterparts on the carriage and carriage casing complementary to the mating parts.