In the linear motion guide unit, a retainer plate for retaining rolling elements, or rollers, is prevented from deformation so as to smoothly guide the rollers. The retainer plate is composed of a retainer member, frame members fitted into respective through holes formed in the retainer member, and a fixing member disposed in a longitudinally extending recess of the retainer member. The frame members form a predetermined gap between the fixing member and a carriage. Tightening forces of fastening bolts are not applied to the retainer member, thereby avoiding deformation of the retainer member.