PURPOSE: To obtain the titled resin product having stabilized qualities, preventing the solidification and degradation of the resin caused by the abnormal reaction, by evaporating and concentrating the resin with an apparatus composed of a specific thin-film evaporator having scraper blades and a concentrate extraction pump having a jacket for the cooling of the concentrate.

CONSTITUTION: The raw material 31 is fed continuously to the thin-film evaporator 11 having scraper blades 10 and an exclusive inlet 44 for a diluent through the raw material inlet 5 and is formed to a thin film by the action of the rotary blades 2. The thin film is transferred downward through the gap 41, and the volatile component is evaporated with the heat transfer body heated with the jacket 3. The concentrate is transferred downward by the action of the scraper blades 10, introduced into the extraction pump 20, and taken out through the outlet 6 as the concentrate 35. A diluent is introduced into the evaporator through the diluent inlet 44 to prevent the abnormal reaction of the concentrate or to adjust the viscosity of the concentrate.