A shaft seal mechanism (10,10c;50,70) configured to seal a gap between a stator which surrounds an outer circumference of a rotor of a rotary machine (1;2) and the rotor, and divides the gap into a fluid low pressure region on one side of the rotor in an axial direction and a fluid high pressure region on other side of the rotor in the axial direction, the shaft seal mechanism comprising: an accommodation body which is provided in the stator and in which an accommodation space extending in a circumferential direction is formed and an opening of the accommodation space is formed toward the outer circumference of the rotor; a seal body which includes a plurality of thin plate seal pieces which are overlapped with minute gaps to each other in the circumferential direction of the rotor and in which a radially outward end side is accommodated in the accommodation space of the accommodation body and a radially inward end extends toward the outer circumference of the rotor from the opening; a plate body (17,17A) which covers the one side end of the seal body in the axial direction and in which a plate surface of the plate body facing the one side in the axial direction is pressed to an inner wall surface of the accommodation body facing to the plate surface in the axis direction by a pressure of the fluid; and characterised in that it further comprises: a recessed-protruding portion (30,60) which is formed on at least one of the plate surface of the plate body and the inner wall surface of the accommodation body and which includes a recessed portion (31,61) which extends from the radially inward side toward the outward side and is recessed in the axis direction and a protruding portion (32,62) which projects to the other side from the recessed portion in the radially inward side, wherein the recessed portion (31,61) of the recessed-protruding portion (30,60) connects a pocket to the fluid low pressure region, the pocket being formed between the one of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body and other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body when the protruding portion (32, 62) abuts to the other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body. an accommodation body which is provided in the stator and in which an accommodation space extending in a circumferential direction is formed and an opening of the accommodation space is formed toward the outer circumference of the rotor; a seal body which includes a plurality of thin plate seal pieces which are overlapped with minute gaps to each other in the circumferential direction of the rotor and in which a radially outward end side is accommodated in the accommodation space of the accommodation body and a radially inward end extends toward the outer circumference of the rotor from the opening; a plate body (17,17A) which covers the one side end of the seal body in the axial direction and in which a plate surface of the plate body facing the one side in the axial direction is pressed to an inner wall surface of the accommodation body facing to the plate surface in the axis direction by a pressure of the fluid; and characterised in that it further comprises: a recessed-protruding portion (30,60) which is formed on at least one of the plate surface of the plate body and the inner wall surface of the accommodation body and which includes a recessed portion (31,61) which extends from the radially inward side toward the outward side and is recessed in the axis direction and a protruding portion (32,62) which projects to the other side from the recessed portion in the radially inward side, wherein the recessed portion (31,61) of the recessed-protruding portion (30,60) connects a pocket to the fluid low pressure region, the pocket being formed between the one of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body and other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body when the protruding portion (32, 62) abuts to the other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body. a recessed-protruding portion (30,60) which is formed on at least one of the plate surface of the plate body and the inner wall surface of the accommodation body and which includes a recessed portion (31,61) which extends from the radially inward side toward the outward side and is recessed in the axis direction and a protruding portion (32,62) which projects to the other side from the recessed portion in the radially inward side, wherein the recessed portion (31,61) of the recessed-protruding portion (30,60) connects a pocket to the fluid low pressure region, the pocket being formed between the one of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body and other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body when the protruding portion (32, 62) abuts to the other of the plate surface of the plate body (17,17A) and the inner wall surface of the accommodation body.