resistor r 6 of 51 k u03c9 to a movable terminal of a device 83 for setting the main resin extrusion stop position comprising a variable resistor of 5 k u03c9 one of fixed terminals of the main resin extrusion stop position setting device 83 is connected to a power source of 15 v through a resistor r 7 of 4 7 k u03c9 and the other fixed terminal is grounded through a resistor r 8 of 4 7 k u03c9 a positive terminal of an operational amplifier 82 is grounded through a resistor r 9 of 26 k u03c9 and the output terminal thereof is connected to a base of a transistor tr 1 through a resistor r 10 of 5 k u03c9 the base of the transistor tr 1 is grounded through a resistor r 11 of 10 k u03c9 and an emitter thereof is directly grounded a collector of the transistor tr 1 is connected to a power source of 15 v through a diode d 3 and a exciting coil 74b of the main resin extrusion stop relay 74 connected in parallel with each other the parison control circuit 40 includes first and second auxiliary resin extrusion speed setting devices 91 and 96 each of which comprises a variable resistor one fixed terminal of each of the first and second auxiliary resin extrusion speed setting devices 91 and 96 is connected to a power source.