PURPOSE: To attain continuous manufacture of final products having comparatively narrow distribution of molecular weight and stabilized quality by specifying one stage in each inner capacity between continuous ring, making slit between a stator and a rotor ring to have 3-12 length/width ratio and making the distance between respective rings longer than the width.

CONSTITUTION: This device possesses a cylindrical housing 1 provided with co-current inlet and opened outlet parts 2, 3 for liquid reaction medium and products, and a series of rotor rings 6 mounted on the shaft as freely center rotable state. Each inner capacity between continuous rings is specified with single stage and comparatively narrow slits 7, 8 are remained between the rotor rings 6 and the inner surface of housing 1 and between a stator ring 5 and the outer wall of the shaft 4. In addition, the slits 7, 8 are formed so that the length/width ratio is 3 to 12 and the distance between respective rings 5, 6 toward axial direction is longer than the width.