PURPOSE: To obtain a filter medium excellently well-balanced in filtration accuracy and service life by sticking and joining unwoven fabric composed of an extra fine fiber to unwoven fabric composed of a thicker fiber to make the filter medium.

CONSTITUTION: The unwoven fabric such as spun-bonded unwoven fabric made of polyester having 10-30μm average fiber diameter, 80-200g/m2 METSUKE (unit) weight and 20-200μm average flow rate pore diameter is prepared. And the unwoven fabric B such as melt-blown unwoven fabric made of polyolefin having 1.0-6.0μm average fiber diameter, 10-60g/m2 METSUKE (unit) weight and 5-50μm average flow rate pore diameter is prepared. The unwoven fabric A and the unwoven fabric B are laminated and stuck joined to each other with a powdery resin to make the filter medium having 90-210g/m2 METSUKE (unit) weight and 0.1-1.5mm thickness. The filter medium is lightweighted and excellent in pleating workability and the stripping property of cake layer of material to be filtered after filtration.