Abstract: A mechanism, giving less environmental load, for treating animal fibers of a continuous web form so as not to spoil inherent properties of the animal fibers such as hand-feeling and water repellency, so as to improve resistance to felting (shrinkage) and pilling. The mechanism includes: a tank filled with a treatment liquid; a net-conveyor having upper and lower mesh belts put one upon the other to sandwich the continuous web form therebetween for conveying the web form through the liquid of the tank; a treating-liquid circulation system including a gas-liquid mixing pump connected to a suction-port in the tank and pumping out the liquid, a static mixer connected downstream of the pump, and a discharge nozzle placed at a position in the tank facing the suction-port with the mesh belts therebetween, the discharge nozzle being connected downstream of the mixer; and an ozonizer for supplying ozone gas into the system.