A continuous mixer in which a pair of left and right rotors 4 are rotatably inserted into a chamber 2 having a feed port 13 and a discharge port 14 for materials at both axial ends, respectively, a gate device 17 for adjusting the polymer flow resistance of the materials is provided halfway in the axial direction of the chamber 2, and a first and a second mixing portions 19, 21 are formed at portions, respectively, of the rotors 4 positioned upstream and downstream of the gate device 17, wherein a forced feed means 23 for forcibly post-adding the materials is connected to a portion downstream of the gate device 17 in the chamber 2 and upstream of the discharge port 15.