To provide the subject equipment capable of producing liquid to be treated, in which variation in its molecular weight distribution is small and its deterioration can be avoided, and useful for producing optical polycarbonate or the like, by providing in a reactor an anaxial agitator having doughnut-like disks, disks with openings and conveying plates for coupling these disks.

This polymerization reactor has a cylindrical shape, is placed horizontally and is equipped with an anaxial agitator 9 for agitating liquid A to be treated in the reactor. The agitator 9 has the same axis of rotation as the axis of the reactor 1, plural doughnut-like disks 11 fixed vertically to the axis, two disks 5 each having opening and fixed vertically to the axis in the neighborhood of both ends of the reactor 1, and conveying plates 6 coupling adjacent disks 11 together and coupling the disk 11 with the disk 5, and having a part rotating in the neighborhood of the inner wall of the reactor 1 and having a mechanism for transferring the liquid A from an inlet 2 to an outlet 3 of the reactor.