A device for supplying a cylindrical bottomed preform from an injection molding machine to a biaxial orientation blow molding machine, in which the pieces are conveyed in an upward opening attitude. The pieces are then inverted by an inverting table for inverting the piece from the upward opening to a downward opening attitude. The pieces are horizontally moved into piece guide recesses by an inserting plate and are dropped from the recesses to mandrels of the heat blow molding machine directly under the piece thus conveyed by a stopper plate to assemble the piece thus dropped with the mandrel for the biaxial orientation blow molding process.