The present invention provides a mixed fiber nonwoven fabric with both a small pressure loss and a high dust collection efficiency, particularly a mixed fiber nonwoven fabric that works effectively in air filters, and also provides a filter medium formed thereof.
The mixed fiber nonwoven fabric according to the invention is a mixed fiber nonwoven fabric comprising at least two types of fibers, namely, fibers of polyolefin based resin component A and fibers of polyolefin based resin component B, a fiber group containing fibers of polyolefin based resin component A being referred to as first fiber group, the first fiber group having a number average fiber diameter of 0.3µm to 7.0 µm, part of the fibers of polyolefin based resin component B that have a fiber diameter in the range of 15µm to 100 µm and not less than 5 times the number average fiber diameter of the first fiber group being referred to as second fiber group, the fibers of the second fiber group maintaining a form of fibers and existing in the cross section of the mixed fiber nonwoven fabric at a rate of 7.0 fibers or more per millimeter of the cross-sectional length, the melting point of polyolefin based resin component B being lower by 5°C to 40°C than that of polyolefin based resin component A, and the number average fiber diameter of the mixed fiber nonwoven fabric as a whole being 0.3µm to 10 µm.