An exhaust ventilator has a frame on which an opening is formed. The frame is composed of a main frame and a flange. Partitions divide the opening of the frame into a plurality of air vents in a matrix manner. Butterfly valves of plate shape have their upper end fixed to the partitions. Lower portions of the butterfly valves are able to open and close the air vents. The frame, partitions and butterfly valves are made of the same olefinic material. Thus, they can be recycled without disassembling.