Screw for injection molding machine, injection molding machine, and injection molding method

An injection molding machine comprising:

• a cylinder that is provided with an injection nozzle;
• and
• a screw that is provided inside the cylinder so as to be able to rotate around a rotating axis and to be able to advance and retreat along the rotating axis,
• wherein the injection molding machine performs injection molding of a fiber reinforcing resin, and
• wherein the screw includes:
• a first stage that is provided on an upstream side;
• and
• a second stage that is provided on a downstream side of the first stage,
• wherein the first stage includes a feed zone, a compression zone, and a metering zone in order from the upstream side, the compression zone being provided with a main flight and an auxiliary flight having an outer diameter smaller than the outer diameter of the main flight,
• wherein the second stage includes a multi-start screw portion which is provided on an upstream side and has a plurality of flights, and a kneading portion which is provided on a downstream side of the multi-start screw portion and has a fin, and
• when a diameter of an apex portion of the main flight is D, a length of the screw, in which the multi-start screw portion is provided, in a rotating axis direction ranges from 2 D to 5 D.