That is, when the mean size of pores of the porous support 11, the mean particle diameter of the catalyst and the mean particle diameter of the binder resin are within the ranges defined above, the binder resin solution (or dispersion) fills a deeper area of the porous support 11 due to filtering-like effects, and the catalyst may be formed as a thin layer on the surface of the porous support 11. That is, for the production of the porous support 11 including the first region 13 and the second region 14, in order for the catalyst and the binder resin to selectively permeate the porous support 11, preferably, the mean particle diameter of the catalyst is larger than the mean pore size of the porous support 11 and the mean pore size of the porous support 11 is larger than the mean particle size of the binder resin.

In the specification of the present invention, the depth of the porous support 11 is the same as the thickness of the porous support 11 and increases from one surface of the porous support 11 on which the catalyst layer 12 is disposed to another surface of the porous support 11 on which the catalyst layer 12 is not disposed.

Regarding the first region 13 and the second region 14 of the porous support 11, the first region 13 may be disposed under the catalyst layer 12 and the second region may be disposed under the first region 13, since the catalyst layer 12 permeates into the porous support 11 while filling inner pores from the one surface of the porous support 11.