1. A three-dimensional netted structure comprising: a netted structure being manufactured by preparing a thermoplastic resin as a raw material or a main raw material, wherein said resin is formed into a plurality of helically and randomly entangled, partly and thermally bonded filaments by extrusion molding, wherein said filaments are cooled with a liquid so as to obtain said netted structure, and wherein said netted structure has sparse and dense portions arranged alternately in a direction in which said resin is extruded.