sides of screw shaft 3 are formed in cylindrical chambers 27 27 so that have their axes parallel with screw shaft 3 having an inner wall portion overlapped with the shaft 3 chambers 27 27 being disposed of receiving shafts which will be referred to hereinafter along kneading screw shaft 3 there are grooved two raws of grooves 4 on the outer peripheral surface thereof on the walls forming the grooves there are formed kneading teeth 21 grooved into flat teeth shape in the inside of chambers 27 27 there is alternatively accommodated by manual replacement one of two kinds of shafts subject to the properties of raw resin material selected for a fuller understanding in a certain case both satellite kneading shafts 22 22 are used as shown in fig4 and 5 and in other case both one of the satellite kneading shafts 22 and one of the wall side shafts 28 may be used as shown in fig6 and in a still further case both the wall side shafts 28 28 may be used as shown in fig7 as depicted in fig6 the wall side shafts are elongated cylindrical with continuous outer surfaces with an arc shaped channel or opening extending along the wall axially with a diameter similar to that of shaft 3 the satellite kneading shaft 22 has its outer periphery in contact with the inner wall surface of the chamber 27 the outer periphery being grooved with flat teeth engageable with the kneading teeth 21 of the screw shaft 3 the wall.