To provide a shaft seal device capable of facilitating its assembly and preventing a leakage of dope in an acetylator.

A screw sleeve 12 having a spiral groove 16 at outer periphery is attached in the vicinity of a through part of a rotary shaft 2 passing through a housing to seal in such a way that dope in a machine is pushed back into the inside of the machine by the screw sleeve 12 rotating integrally with the rotary shaft 2. The screw sleeve 12 is formed by dividing it into two parts in the peripheral direction and into three parts in the axial direction, and these divided parts 18, 20, 24, 26, 33, 35 are mutually tightened and are assembled substantially cylindrically at outer periphery of the rotary shaft 2. This assembly work can be done from the outside in the radial direction of the rotary shaft 2 between a bearing device supporting the rotary shaft 2 and the housing to assemble them easily without disassembling the bearing device.