A linear motion guide unit is envisaged smooth transfer of a roller from a turnaround passage to a return passage and vice versa across a joint between the turnaround passage and the associated return passage. Protrusions extending stepwise from an end of the turnaround passage come into complementary fit joints with an associated end of a tubular member defining the return passage to make wall surfaces to guide axially opposite ends of the roller, in which the joints are staggered or different in their locations between wall surfaces. The return passage is defined with a fore-and-aft hole of rectangular shape in transverse section inside a tubular member that fits into a bore made in the carriage. The tubular member is joined at lengthwise opposite ends thereof together to the protrusions that are raised above end surfaces of the end caps to extend the turnaround passage into the bore. Edges of the protrusions come into complementary fit joints with the associated ends of the tubular member to provide wall surfaces to guide axially opposite ends of the roller.