To provide an air filter stably ensuring narrow air passing surface without deforming the pleat shape of a filter medium at a time of the adsorption of matter to be absorbed and easily replaced at a time of replacement by holding the end edge of a filter medium between the end surfaces of a filter outer frame and a filter medium pressing frame.

A filter medium replacing type air filter mainly consists of an air filter outer frame 1, a filter medium pack 2 and a filter medium pressing frame 3. The air filter outer frame 1 has a filter medium terminal receiving jig 5 receiving the terminal of the filter medium of the filter medium pack 2 provided to the entire inside periphery thereof and the upper and lower side surfaces of the jig 5 are linear end surfaces 4'' and the left and right surfaces thereof have end surfaces 4' having a pleated shape fitted to that of the filter medium. The end edges 4', 4'' of the filter medium are held between the filter medium terminal receiving jig and the filter medium pressing frame 3 having end surfaces 3', 33' having a shape corresponding to that of the end surfaces 5, 5'' of the jig 5 to hold the pleated shape of the filter medium to protect the filter medium from deformation. By this constitution, a narrow air passing surface can be stably and effectively put to practical use and, by replacing only the filter medium pack, the air filter can be renewed.