PURPOSE: To provide an air filter capable of satisfying the capacity of a medium capacity filter through the packing rate of a filter medium is low as compared with a conventional filter, enabled in compact planning and capable of being reduced in the volume of waste after use.

CONSTITUTION: An air filter is formed by arranging a plurality of bag-shaped filter mediums in an outer frame in a freely replaceable manner so as to orient the opening parts of them on the upstream side in an air stream direction and each of the filter mediums 1 is a laminated filter medium consisting of an upstream side non-electret coarse layer 1a and a downstream side electret dense layer 1b.