The concentration of a sealed fluid in the vicinity of a sliding face between a stationary-side seal ring and a rotating-side seal ring is prevented without increasing the number of components and without providing a large-scale external circulation device. A seal cavity includes a radial sliding bearing 11, 25 for supporting a rotating shaft 2, and a sealing means 4, 30 on the side opposite to a sealed fluid source of the radial sliding bearing 11, 25 in a rotation axis direction, for sealing a sealed fluid. Fluid introduction holes 20 are provided in the radial sliding bearing 11, 25 for connecting the sealed fluid source side and the vicinity of the sealing means 4, 30 on the high-pressure fluid side.