To provide a seal device which, even if adopted in a rotary table device, can continuously maintain a high level of sealing properties in the machining of a workpiece.

A seal mechanism 1 is provided between a circular table 12 and a frame 10 in a rotary table device. One of a surface of the circular table 12 and a surface of the frame 10 which face each other has an annular groove 2 which is opened to the other of the surfaces with a shaft line of a rotating shaft 11 as a center. Both side surfaces of the groove 2 are formed of permanent magnets 5 having magnetic poles which are opposite to each other. The inside of the groove 2 is filled with a magnetic fluid 3. The other surface has a partition plate 4 that is protruded from the other end face which faces the groove 2. At least the front end of the partition plate is immersed in the magnetic fluid 3 in the groove 2. The partition plate is annularly arranged with the shaft line of the rotating shaft 11 as a center.