A linear motion guide unit is disclosed in which there is provided a retainer band making it possible to easily fit a roller chain with rollers traveling through a recirculation circuit into a load way of the recirculation circuit, thereby making sure of smooth recirculation of the roller chain. Cooperation of the retainer band with a retainer plate helps guide links of the roller chain in a load way of the recirculation circuit, keeping the roller chain against running out of the load way thereby ensuring smooth movement of the roller chain throughout the recirculation circuit.