PURPOSE: To provide a seal device allowing no micro particles of dirt to deposit on ring-shaped packing.

CONSTITUTION: Three pieces of lip packing 10a∼10c are arranged on a shaft sleeve 2. Each packing is sandwiched between two support rings 4∼7. The support rings are coupled with each other and fixed on the vessel body as a whole. A ring-shaped chamber 9 opening toward sea water W is formed in the utmost outer support ring 7. A ring-shaped member 8 for removing dirt, having a U-shaped axial section is arranged in front of the chamber opening, with one foot 8a fixed on the sleeve in a manner of being capable of rotating together therewith and the other foot 8b contacting the front of the support ring 7. The foot 8b has a wing 12. The interior of the chamber is brought into low pressure condition by the rotation of the wing. Porous regions are formed in walls forming the chamber. Flow of sea water is generated by the sea water flowing from the outside sea through the porous regions to the chamber. dirt particles are absorbed in the porous regions.