AIR FILTER FILTERING MEDIUM, FILTER PLEAT PACK, AND AIR FILTER UNIT

A provided air filter medium is an air filter medium including a porous fluorine resin membrane, the air filter medium further including: a collection layer; and an air-permeable adhesive layer. The collection layer, the air-permeable adhesive layer, and the porous fluorine resin membrane are placed in this order from upstream to downstream of the filter medium configured to allow an air flow to pass through the filter medium. An initial pressure drop of the filter medium at a permeate flow rate of 5.3 cm/sec is 250 Pa or less. When a test is performed in which polydisperse polyalphaolefin particles having a peak in number in a particle size range of 0.1 to 0.2 µm are allowed to pass through the filter medium at a concentration of 0.2 to 0.5 g/m3 and a linear velocity of 5.3 cm/sec and a holding amount of the particles held by the filter medium and a variation of a pressure drop of the filter medium are evaluated, the holding amount is 43.0 g/m2 or more from a moment when the holding amount reaches 20 g/m2 to when a moment the pressure drop reaches PD1 + 120 Pa, where PD1 is the pressure drop of the filter medium at the moment when the holding amount reaches 20 g/m2. This air filter medium has a reduced initial pressure drop and is suitable for use in an environment including liquid particles.