PURPOSE:To obtain foamed resin particles within a narrow space without causing blocking due to the fusing of the particles, by dispersing thermoplastic resin particles containing a volatile foaming agent into water, heating the dispersed matters under pressure, and releasing said dispersed matter into water under reduced pressure. CONSTITUTION:The thermoplastic resin particles containing a volatile foaming agent are dispersed into water in a pressure container 1, then after the dispersed matter is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin under a pressure equal to or higher than the vapor pressure of the volatile foaming agent, the dispersed matter is released into water in a container 5 in which the pressure is lower than the first mentioned pressure to allow the particles to float on the water, and the particles are recovered.
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