Apparatus to make decorations on a prefabricated water-proofing bitumen-mix membrane, wherein the decorations are made by depositing solid particles, in the form of flakes, grains, sand or grit, suitable to adhere to at least one surface of said prefabricated water-proofing bitumen-mix membrane. The apparatus includes at least one transfer member provided with a support surface suitable to receive, support and transfer the solid particles toward the surface to be enhanced of the prefabricated water-proofing bitumen-mix membrane. The support surface is provided with a plurality of cavities suitable to receive the solid particles. The cavities are made inside at least one surface portion of the support surface and the surface portion, essentially reproducing the shape and sizes of at least one of the decorations.