An injection molding machine to which a resin raw material is fed on an upstream side and to which reinforcing fibers are fed on a downstream side, the injection molding machine comprising: a cylinder at which a discharge nozzle has been formed; a screw provided rotatable and movable in a rotation axis direction inside the cylinder a resin feed portion that feeds the resin raw material in the cylinder; and a fiber feed portion that is provided closer to a downstream side than the resin feed portion, and feeds the reinforcing fibers in the cylinder, wherein the screw comprises: a first stage at which the resin raw material which is fed is melted; and a second stage that continues to the first stage and comprises a feed portion, a compression portion closer to the downstream side than the feed portion, and a measurement portion closer to the downstream side than the feed portion and the compression portion, and at which the melted resin raw material and the fed reinforcing fibers are mixed with each other, wherein a flight provided at the second stage includes: a large-diameter flight with a relatively large outer diameter, the injection molding machine being characterized in that the flight includes a small-diameter flight with a relatively small outer diameter; and a resin passage formed with a gap between a top portion of the small-diameter flight and the cylinder and in which a backflow of the melted resin raw material is generated from a screw groove of the downstream side toward a screw groove of the upstream side of the screw. a cylinder at which a discharge nozzle has been formed; a screw provided rotatable and movable in a rotation axis direction inside the cylinder a resin feed portion that feeds the resin raw material in the cylinder; and a first stage at which the resin raw material which is fed is melted; and a second stage that continues to the first stage and comprises a feed portion, a compression portion closer to the downstream side than the feed portion, and a measurement portion closer to the downstream side than the feed portion and the compression portion, and at which the melted resin raw material and the fed reinforcing fibers are mixed with each other, wherein a flight provided at the second stage includes: a large-diameter flight with a relatively large outer diameter, the injection molding machine being characterized in that the flight includes a small-diameter flight with a relatively small outer diameter; and a resin passage formed with a gap between a top portion of the small-diameter flight and the cylinder and in which a backflow of the melted resin raw material is generated from a screw groove of the downstream side toward a screw groove of the upstream side of the screw. a large-diameter flight with a relatively large outer diameter, the injection molding machine being characterized in that the flight includes a small-diameter flight with a relatively small outer diameter; and a resin passage formed with a gap between a top portion of the small-diameter flight and the cylinder and in which a backflow of the melted resin raw material is generated from a screw groove of the downstream side toward a screw groove of the upstream side of the screw.