PURPOSE: To obtain a casting mold at low production cost with excellent strength by a method in which a porous layer is composed of the integral molding layer in which granular fillers are combined with fine porous resin from the front surface of the layer facing a casting space to the rear surface thereof, and the grain size of the filler changes to coarse grain from fine grain with advancing to the rear surface of the layer from the front surface thereof.

CONSTITUTION: In the casting molds 22, 23 in which a casting space is formed with the porous layer having a plurality of fine holes inside of a supporting frame, the porous layer is composed of the integral molding layer in which granular fillers are combined with fine porous resin from the front surfaces 22a, 23a of the layer to the rear surface thereof. The grain size of the filler changes from fine grain to coarse grain with advancing from the front surfaces 22a, 23a of the layer to the rear surface thereof in the distribution on the cross section of the porous layer. Since in the integral molding layer, granular fillers are combined with the fine porous resin, it is excellent in strength due to nonmechanically connected parts in the porous layer. Further, since the grain size-distribution in the filler changes to coarse grain from fine grain with advancing from the front surface of the layer to the rear surface thereof, the distribution of many fine holes opening on the surface of the porous layer as a filtration surface, is caused to be fine and uniform.