3. A three-dimensional netted structure having an upper surface, a lower surface, two side surfaces, a left end surface, and a right end surface, the structure comprising a plurality of filaments helically and randomly entangled and thermally bonded together, wherein:said plurality of filaments are formed out of a thermoplastic resin by extrusion molding followed by cooling in a liquid; andsaid upper surface, said lower surface, and said two side surfaces are molded; said upper surface, said lower surface, and said two side surfaces are flat; regions of the three-dimensional netted structure, which extend a predetermined distance from said upper surface, said lower surface, and said two side surfaces into an inner portion of the three-dimensional netted structure are compressed; and a density of said regions is higher than a density of said inner portion of the three-dimensional netted structure.