A linear motion guide unit where there is provided a tiny mechanism to keep a cage retaining therein more than one rolling element against wobbling. The cage retaining rolling elements holds therein a pinion, which mates with racks lying in the raceway grooves. A pinion holder is allowed to snap into a hook hole formed in the cage. To this end, the pinion holder has a flange extending out of any side of the pinion holder so as to come into abutment against any one surface of an edge around the hook hole, and an snap hook extending out of the other side of the pinion holder to come into engagement with another surface of the edge around the hook hole.