An inside seal is installed in a recess open downward in the slider to keep load-carrying races kept free of foreign materials that have already crept into the inside of the slider. The inside seal is composed of a metallic core and a sealing member that includes a joint portion secured to the core and a major portion integral with the joint portion. The joint portion has a mating surface to come into engagement with a downward surface deep inside the recess cut in a carriage while the major portion includes a first lip to come into sliding engagement with a guide rail, a second lip come into abutment against an inward sidewall of the recess, and third lip to come into abutment against the downward surface.