A linear motion guide unit restrains fluctuations in sliding friction and generation of heat by correcting the postures of rollers having been inclined in a no-load area such that their axes become orthogonal to a guide surface of a carriage to thereby introduce the rollers in proper postures into a load area. A retainer plate of the guide unit has a guide surface for guiding end surfaces of the rollers and has protrusions protruding from the guide surface at its opposite end portions facing crownings of the carriage. The rollers rolling from a turnaround passage to a load-carrying race are pressed by the protrusions toward the guide surface of the carriage so as to be arrayed in such a posture that the axes of the rollers become orthogonal to the guide surface on the inlet side of the crowning of the carriage, whereby the occurrence of roller skew is prevented.