A twin screw extruder (10) for producing a fiber-reinforced resin composition, which is obtained by charging the extruder with a thermoplastic resin and reinforcing fibers in roving form and the reinforcing fibers being fibrillated/cut and being dispersed/kneaded into the thermoplastic resin, comprises: a plate-shaped blade (15), which protrudes from the inner surface of a cylinder (11) and faces a screw (20) and the longitudinal direction of which faces the axial direction of the cylinder; and a height adjustment means (16) for adjusting the gap between the blade (15) and the screw (20).