A unidirectionally reinforced resin structure is manufactured by an apparatus which comprises a melt resin bath in which a melt resin is stored and into which a long fiber bundle passes, and a plurality of opening pins disposed in the melt resin bath. The long fiber bundle is impregnated with the melt resin and opened by the opening pins during the passing in the melt resin bath. The opening pins are arranged in a perpendicular direction with respect to the melt resin bath and the opening pins are composed of at least two groups in the perpendicular direction so as to open at least two long fiber bundles.