PURPOSE: To provide a multilayer structured filter with enhanced dust collecting efficiency, obtained by a method wherein a filter mainly charged with positive charge and a filter mainly charged with negative charge are stacked and fibers between both filter layers are mutually entangled to integrate said layers.

CONSTITUTION: A non-woven fabric made of wool and a non-woven fabric made of polypropylene having a thickness of about 1/2 to a conventional filter (about 3mm thickness usually) is used. The non-woven fabric made of wool can be positively charged as the whole by resin processing and, on the other hand, polypropylene can be negatively charged. These positively and negatively charged thin non-woven fabrics made of wool and polypropylene are alternately stacked on every one layer or more and integrated by subjecting the same to needle punching to entangle fibers between layers. By this method, dust collecting efficiency is made uniform to enhance collection efficiency as well as to impart pile filtering characteristics and the life can be prolonged to a large extent.