To improve performance by coating both surfaces of a plastic film with molten asphalt while specifying a penetration and overall thickness and molding the plastic film in a sheet shape.

A plastic film 2 as a core layer is immersed into an asphalt thermally fused article having a penetration of 5-40 and asphalt layers 3 are attached onto both surfaces, and fine sand 4, etc., are sprayed against the surfaces of the layers 3 and the whole is roll-molded in thickness of 0.5-10 mm while preventing the adhesion of the layers 3 onto a roll, thus forming the waterproof mat 1. Holes having a specified diameter are formed to the film 2 at regular intervals in a cold district, and the mutual layers 3 on both surfaces of the film 2 are connected and the detaching of the layers from the film 2 is obviated. The mat 1 is buried between a draining surface layer and a base layer, and rainwater infiltrated into the surface layer is stopped by the mat 1 and drained to a catch basin, etc., by a distributing pipe buried on both sides of a road at the time of the execution of works. Accordingly, since asphalt works as adhesives under a heated and molten state, the adhesion of the base layer and the surface layer can be ensured, and waterproofness is carried out completely.