A linear motion device includes a guiding member extending along a first direction and a slide block assembly slidably disposed on the guiding member. The slide block assembly includes a slide block, two ball race members at two sides of the slide block, two circulation members at two sides of the slide block along the first direction, and two end covers assembled on the circulation members. One or more of the circulation members has two revolve channel members. The revolve channel member has an upper protrusion member and a lower protrusion member protruding out of the upper protrusion member. Since the protruding portion of the lower protrusion member can be served as the bottom surface of the revolve curve, stepped structures caused by assembling or component tolerances are not formed between the bottom surface and nearby portions, and the balls can roll stably in the linear motion device.