PURPOSE: To prevent film-out phenomenon by forming core part excavated with many slits in welded metal corrugated plate and flat plate, thereafter by directly forming wash-coat layer and by impregnating metal catalyst on the layer.

CONSTITUTION: When the metal corrugated plate 31 and flat plate 33 are overlapped and rolled in multilayer, and the surfaces thereof are irradiated with laser beam 37. As this result, the corrugated plate 31 and flat plate 33 are welded at the irradiated points and thereby the film-out phenomenon can be surely prevented. Since the corrugated plate 31 and flat plate 33 are excavated with many slits 41 by projecting with laser beam 37, the wash-coat liq. 44 is surely attached around the slits 41 due to the function of slit, by immersing the core part 35 made from the corrugated plate 31 and flat plate 33 with the slits 41, in the wash-coat liq. 44.