A shaft seal mechanism (leaf seal) by which a desired seal performance can be stably obtained is provided. The shaft seal mechanism is constructed such that a plurality of thin plates are arranged in an annular space between a rotor and a stator so as to form an annular thin plate assembly, the thin plates have their outer circumferential proximal end side supported to the side of the stator and their inner circumferential distal end side non-fixed to an outer circumferential surface of the rotor so that the annular thin plate assembly divides the annular space between the rotor and the stator into a higher pressure side area and a lower pressure side area. An activating member is integrally provided on the side of the annular thin plate assembly. The activating member supports the annular thin plate assembly to be levitated coaxially with the rotor. A large size fluid machine including such a shaft seal mechanism is also provided.
