A shaft sealing mechanism that, by being disposed in an annular space formed between a fixed part and a rotating shaft, partitions the annular space into a high-pressure-side region and a low-pressure-side region to prevent fluid from flowing from the high-pressure-side region toward the low-pressure-side region in the annular space in a direction of the rotating shaft, characterized in that the shaft sealing mechanism comprises: an annular seal housing disposed at an inner circumferential portion of the fixed part; a plurality of thin-plate seal pieces stacked and disposed annularly in a circumferential direction of the rotating shaft, each of which has an outer-circumferential-side proximal end, the proximal ends being fixed to the seal housing by means of a pair of high-pressure-side and low-pressure-side retainers (23, 24), an inner-circumferential-side distal end being a free end and forming an acute angle with an outer circumferential surface of the rotating shaft, and a width dimension in the direction of the rotating shaft; an annular high-pressure-side plate held between high-pressure-side side edges of the thin-plate seal pieces facing the high-pressure-side region and high-pressure-side retainer so as to form a gap (δH) between the high-pressure-side plate and the seal housing in the direction of the rotating shaft, an inner-circumferential-side distal end of the high-pressure-side plate being positioned outward of the inner-circumferential-side distal ends of the thin-plate seal pieces in the radial direction of the rotating shaft; and an annular low-pressure-side plate held between the seal housing and low-pressure-side side edges of the thin-plate seal pieces facing the low-pressure-side region so as to form a gap (δL) between the low-pressure-side side edges and the seal housing in the direction of the rotating shaft, an inner-circumferential-side distal end of the low-pressure-side plate being positioned outward of the inner-circumferential-side distal end of the high-pressure-side plate in the radial direction of the rotating shaft, wherein each of the thin-plate seal pieces has one or more thick parts (31 to 33) which have a uniform thickness that is larger than the thickness of any other part of the thin-plate seal piece, the thickness extending in a direction perpendicular to a lower surface and an upper surface of the thin-plate seal piece, the lower surface facing the rotating shaft, the upper surface being opposed to the lower surface, and wherein the one or more thick parts (31 to 33) are formed such that an outer-circumferential-side end of each thick part (31 to 33) is positioned inward of the inner-circumferential-side distal end of the low-pressure-side plate in the radial direction of the rotating shaft, characterized in that the one or more thick parts are formed intermittently along the low-pressure-side side edge as multiple thick parts to be apart from one another and aligned in radial direction of the rotating shaft. an annular seal housing disposed at an inner circumferential portion of the fixed part; a plurality of thin-plate seal pieces stacked and disposed annularly in a circumferential direction of the rotating shaft, each of which has an outer-circumferential-side proximal end, the proximal ends being fixed to the seal housing by means of a pair of high-pressure-side and low-pressure-side retainers (23, 24), an inner-circumferential-side distal end being a free end and forming an acute angle with an outer circumferential surface of the rotating shaft, and a width dimension in the direction of the rotating shaft; an annular high-pressure-side plate held between high-pressure-side side edges of the thin-plate seal pieces facing the high-pressure-side region and high-pressure-side retainer so as to form a gap (δH) between the high-pressure-side plate and the seal housing in the direction of the rotating shaft, an inner-circumferential-side distal end of the high-pressure-side plate being positioned outward of the inner-circumferential-side distal ends of the thin-plate seal pieces in the radial direction of the rotating shaft; and an annular low-pressure-side plate held between the seal housing and low-pressure-side side edges of the thin-plate seal pieces facing the low-pressure-side region so as to form a gap (δL) between the low-pressure-side side edges and the seal housing in the direction of the rotating shaft, an inner-circumferential-side distal end of the low-pressure-side plate being positioned outward of the inner-circumferential-side distal end of the high-pressure-side plate in the radial direction of the rotating shaft, wherein each of the thin-plate seal pieces has one or more thick parts (31 to 33) which have a uniform thickness that is larger than the thickness of any other part of the thin-plate seal piece, the thickness extending in a direction perpendicular to a lower surface and an upper surface of the thin-plate seal piece, the lower surface facing the rotating shaft, the upper surface being opposed to the lower surface, and wherein the one or more thick parts (31 to 33) are formed such that an outer-circumferential-side end of each thick part (31 to 33) is positioned inward of the inner-circumferential-side distal end of the low-pressure-side plate in the radial direction of the rotating shaft, characterized in that the one or more thick parts are formed intermittently along the low-pressure-side side edge as multiple thick parts to be apart from one another and aligned in radial direction of the rotating shaft.