The invention provides an apparatus for continuously and efficiently treating volume-reduced polystyrene resin in gel state, thereby removing solvent and recovering resin. A volume-reduced gel-state polystyrene resin is heated in the separation/recovery apparatus under ambient pressure or reduced pressure, for removal of solvent and recovery of resin. The apparatus includes an apparatus main unit 10 having at the top of the unit a solvent-recovering section for continuously recovering evaporated solvent and having at the bottom of the unit a resin-recovering section for recovering the solvent-removed resin; a heating medium flow pipe 20 provided inside the apparatus main unit 10 for allowing flow of a heating medium inside the pipe; a gel-state resin-feeding means 14 for feeding the volume-reduced polystyrene resin in gel-state such that the resin is brought into contact with the heating medium flow pipe 20; a resin-holding section 13 provided in the bottom of the apparatus main unit 10 for holding the resin flowed down to the member after contact with the heating medium flow pipe 20; a heating means 25 for heating the resin held in the resin-holding section 13; and a stirring means 26 for stirring the resin contained in the resin-holding section.