An air filtering device includes an inner seat member, an outer seat member, and a multi-layer filter medium. The inner seat member has opposed first and second sides and a plurality of first air passages extending therethrough from the first side to the second side. The outer seat member has opposed third and fourth sides and a plurality of second air passages extending therethrough from the third side to the fourth side. The multi-layer filter medium is sandwiched between the second side of the inner seat member and the third side of the outer seat member. The multi-layer filter medium has a polypropylene fabric layer, a far-infrared radiation material layer, and an activated carbon fiber layer connected to one another. The first air passages are registered with the second air passages.