Abstract: A roller door is provided with a flexible door leaf, wound on a winding roller which is mounted rotatably above the door opening. Fast with the winding roller is at least one drum on which there is wound, in contrary direction to the door leaf, a flexible traction member (belt, rope, chain) which is loaded with a counterweight for balancing the weight of the door leaf. In order also to tauten the door leaf, with a separation of the functions of weight compensation and tautening of the door leaf, there is integrally rotatably connected with the winding roller at least one second drum on which is wound, in contrary direction to the door leaf, a further flexible traction member (belt, rope, chain) guided around a guide roller, which is mounted stationarily at the base of the door opening, and connected with the door leaf, and a tensioning roller presses with a transverse force against the portion of the further traction member which runs between its drum and the guide roller.