The present invention relates to a resin-molded article with a spring structure, and to a method and apparatus for preparing a superficial layer of such a resin-molded article with a spring structure which has surfaces free from undulations, comprises fused filaments whose fusion is resistant to separation, maintains its cushioning activity and strength even after long use. A water flows from a cooling water outlet 53b into a space between a water-permeating sheet 55 and an inclined plate 51a. Some part of the flowing water C penetrates the water-permeating sheet 55 to appear on its top surface to form there an overlying current M on which receives lengthwise arranged peripheral continuous filaments, and agitates them to cause adjacent filaments to contact each other, to be entwined and gathered, thereby enabling the formation of a superficial layer of the three-dimensional structure 3.