A robot traveling duct for clean room in which a vertical laminar flow of air is produced from a ceiling filter toward a floor thereof, and in which the robot traveling duct is arranged within the clean room and below the ceiling filter and surrounds a guide rail of the robot, the robot traveling duct including a longitudinal opening for connection between the guide rail and the robot. The robot traveling duct includes a first enclosure for enclosing the guide rail to extend along the guide rail, the first enclosure having an air intake system for introducing air, issuing from the ceiling filter, into the first enclosure. The robot traveling duct further includes a second enclosure mounted to the first enclosure to be located below the first enclosure, the second enclosure including a second enclosure filter for filtering air therein and allowing the filtered air to go downwards into the clean room, the second enclosure extending along the guide rail and being equal in width to the first enclosure. The robot traveling duct is further provided with an air forcing mechanism for forcing air from the first enclosure into the second enclosure, whereby a laminar air flow is substantially produced just below the second enclosure means by actuating the air forcing mechanism.