PURPOSE: To control an increase in the initial pressure drop of the titled medium and to obtain a medium-performance filter medium for an air filter provided with a high a layer-to-layer adhesive property by overlapping a staple web cong. hot-melt fibers on an electret raising nonwoven fabric, and hot-pressing both materials.

CONSTITUTION: A staple web contg. at least 30% hot-melt fiber and having ≤0.05% fiber packing rate is overlapped on an electret raising nonwoven fabric composed of whiskery fibrous fluff having at least 3mm length from the surface of the nonwoven fabric and raised over the whole surface of the nonwoven fabric. When both materials are overlapped with the raising surface of the nonwoven fabric as the adhesion surface, the raising fluff eats into the staple web, the respective fibers are tangled with each other, and a layer-to-layer adhesive property stronger than the surface adhesion by the mere melting due to hot pressing can be obtained. Hot press is carried out at ≤1kg/cm2 pressure and at a temp. lower than the m.p. of the electret raising nonwoven fabric and higher than the m.p. of the hot-melt fiber.