A blow mold high-pressure switching step in a blow molding process of an injection stretch blow molding machine is arranged at the first half portion of the blow molding process, to shorten the injection molding process and improve the moldability. The blow mold high-pressure switching step 61B3 of increasing a mold clamping force for blow molds which have been closed in a blow molding process 61B is configured to be performed at a timing within a time from the start of the upper/lower mold opening step 62A1 for opening upper and lower molds in the injection molding process 62A to release a preform 3P to the completion of the injection mold high-pressure switching step 62A3 for increasing the mold clamping force for the closed injection molding mold.

A blow mold high-pressure switching step in a blow molding process of an injection stretch blow molding machine is arranged at the first half portion of the blow molding process, to shorten the injection molding process and improve the moldability. The blow mold high-pressure switching step 61B3 of increasing a mold clamping force for blow molds which have been closed in a blow molding process 61B is configured to be performed at a timing within a time from the start of the upper/lower mold opening step 62A1 for opening upper and lower molds in the injection molding process 62A to release a preform 3P to the completion of the injection mold high-pressure switching step 62A3 for increasing the mold clamping force for the closed injection molding mold.

A blow molding apparatus includes a machine bed, an upper base disposed at intervals in a vertical direction from the machine bed, a transport plate configured to rotate at a height position of the upper base to convey the preform between an injection molding part and a blow molding part, and an elevation mechanism configured to move the transport plate or the upper base up and down in the vertical direction with respect to a mold disposed on the machine bed. A support pillar includes a height adjusting part configured to adjust a stroke of the transport plate or the upper base in the vertical direction with respect to the machine bed.

Moving servo motors of molds in synchronization with the operations of platens which enables fine patterns or shapes to be formed even on a large molded article. A mold clamping device forms patterns or the like on a molded article by detecting a mold position of a second platen among first, second, third platens with digital mold opening/closing position detector, and driving servo motors for molds of the molds in synchronization with a digital mold opening/closing position signal from the digital mold opening/closing position detector.

A blow molding apparatus includes a machine bed, an upper base disposed at intervals in a vertical direction from the machine bed, a transport plate configured to rotate at a height position of the upper base to convey the preform between an injection molding part and a blow molding part, and an elevation mechanism configured to move the transport plate or the upper base up and down in the vertical direction with respect to a mold disposed on the machine bed. A support pillar includes a height adjusting part configured to adjust a stroke of the transport plate or the upper base in the vertical direction with respect to the machine bed.

Moving servo motors of molds in synchronization with the operations of platens which enables fine patterns or shapes to be formed even on a large molded article. A mold clamping device forms patterns or the like on a molded article by detecting a mold position of a second platen among first, second, third platens with digital mold opening/closing position detector, and driving servo motors for molds of the molds in synchronization with a digital mold opening/closing position signal from the digital mold opening/closing position detector.