Abstract: Apparatus for reefing sails on a boat and specially-designed boom including such an apparatus. The hollow boom extrusion houses at least one traveler block with two pulley wheels, over which pass the reefing leech line and the reefing luff line. The apparatus makes it possible to take one or more reefs in the sail simply by pulling on the free end of the reefing luff line which leads to the cockpit of the boat.