PROBLEM TO BE SOLVED: To maximize the deposition amount of titanium oxide while preventing an increase in flow passage resistance by forming a titanium oxide layer of an on-vehicle air cleaning filter formed by coating the entire surface of a honeycomb type active carbon cell base material with the titanium oxide layer in such a manner that the layer is thick in a blasting direction and is thin in a direction orthogonal with the blasting direction. SOLUTION: The honeycomb type active carbon cell 1 as the active carbon porous base material is immersed into a TiO2 sol and is then dried, by which the entire surface of the cell 1 is uniformly coated with the titanium oxide layer. Next, a TiO2 slurry is sprayed to both end apertures of the honeycomb type active carbon cell 1 and is dried. The first titanium oxide layer is formed at a film thickness substantially equal to the opening wall surface, i.e., the surface parallel to an air flow direction in order for the uniform permeation of the air in the forming material of the honeycomb type active carbon cell 1. The second titanium oxide layer in the blasting direction at the opening peripheral edge of the honeycomb type active carbon cell 1 increases the titanium oxide deposition amount at the opening wall surface of the cell and maximizes the deposition amount of the titanium oxide.
