A linear motion rolling contact guide unit having a rod rail having a substantially circular cross section is provided. The guide unit also includes a slider slidably mounted on the rod rail and a plurality of rolling members interposed between the rod rail and the slider to thereby provide a rolling contact therebetween. The slider is so structured that it surrounds only a part the circumference of the rod rail and thus the slider has a generally U-shaped cross sectional shape. Since the rod rail is not surrounded completely, it may be placed in a V-shaped groove of a bed substantially over its entire stroke.