The purpose of the present invention is to provide a shaft seal mechanism that, even if pressing force is applied to thin-plate seal pieces, can suppress deformation due to the pressing force and prevent abrasion due to contact with a rotating shaft in the thin-plate seal pieces. In order to achieve the foregoing, a shaft seal mechanism (11) that blocks a fluid (G) flowing within a ring-shaped space (14) is equipped with: a ring-shaped seal housing (21) disposed on a fixed section (12); a plurality of thin-plate seal pieces (22) that are secured to the seal housing (21), are in sliding contact with a rotating shaft (13), and are layered in a ring shape; a ring-shaped high-pressure-side plate (25) that forms a high-pressure-side gap (´H) between itself and the seal housing (21); a ring-shaped low-pressure-side plate (26) that forms a low-pressure-side gap (´L) between the seal housing (21) and the thin-plate seal pieces (22); stepped sections (31, 32) that are formed on side edge sections (22c, 22d) of the thin-plate seal pieces (22); and locking sections (25b, 26b) that lock the stepped sections (31, 32).