Abstract: A machine for solid phase polymerization comprises: a system for supplying particles of a synthetic polymer; a reaction system for effecting solid phase polymerization of the particles, fed from the supplying system, under a vacuum and heated condition; and a system for discharging the solid phase polymerized particles. The supplying system includes a pre-treatment apparatus comprising: a pre-crystallizer of a vertical agitator type; and a beater of a horizontal type. The reaction system includes a horizontal reaction vessel having a horizontal rotary shaft with a helically formed screw vane. The screw vane has a multiplicity of small through-apertures, and scrapers extend axially extending between adjacent screw vane portions. Intermediate pots having specially designed vacuum breakers are disposed at locations between the reaction system and the supplying system and between the reaction system and the discharging system.