An air filter medium includes a first porous PTFE membrane and a second porous PTFE membrane. An average fiber diameter of fibers included in the first porous PTFE membrane is 0.24 to 0.45 μm, an average fiber diameter of fibers included in the second porous PTFE membrane is 0.04 to 0.23 μm, the air filter medium has a first main surface and a second main surface, and the first porous PTFE membrane and the second porous PTFE membrane are arranged so that an air flow moving from the first main surface to the second main surface passes through the first porous PTFE membrane and subsequently through the second porous PTFE membrane.