A small-sized finite linear motion guide unit is provided in which there is provided a rack-and-pinion arrangement to prevent any discrepancy between retainer plates to make sure of relative sliding movement of guideways. A rack is composed of teeth portions and a pair of connecting bars to fasten the teeth thereon. The connecting bars are different in widthwise length to form asymmetrical shapes. The grooves for a rack made on the guideway includes a middle groove to get the rack to mate with the pinion, and sidewise grooves lying on both sides of the middle groove and having the connecting bars different in widthwise length to make an asymmetric shape.