Provided is a filter medium including a porous polytetrafluoroethylene (PTFE) membrane and a gas-permeable supporting member that are integrated to ensure sufficient stiffness, having excellent gas permeability, and providing excellent bonding between respective layers included in the filter medium. The gas-permeable supporting member includes a substrate having gas-permeability; and a fiber layer that is placed on the substrate so as to be in contact with the porous PTFE membrane. The gas-permeable supporting member has a structure in which fibers of the fiber layer enter into the substrate and are entangled with the substrate so that the fiber layer is bonded to the substrate. The fiber layer contains polyolefin-containing fibers that are bonded to the porous membrane.