pieces 22 can be set in accordance with the quantitative relationship between the size of the high pressure side gap u03b4h and the size of the low pressure side gap u03b4l in the shaft seal mechanism 11 according to the present invention the radial gap size between the inner circumferential side distal end section 26 a of the low pressure side plate 26 and the outer circumferential surface of the rotating shaft 13 is greater than the radial gap size between the inner circumferential side distal end section 25 a of the high pressure side plate 25 and the outer circumferential surface of the rotating shaft 13 in order to yield stable lifting up force with this configuration while the rotation of the rotating shaft 13 is stopping the inner circumferential side distal end sections 22 b of the thin plate seal pieces 22 are in contact with the outer circumferential surface of the rotating shaft 13 at the predetermined preload on the other hand while the rotating shaft 13 is rotating lifting up force is applied to the thin plate seal pieces 22 by the pressure difference due to relative positional shift in the pressure distribution between the top and bottom surfaces of the thin plate sheet pieces 22 and by dynamic pressure effect of the fluid g.