A seal device for a turbine is disposed around a rotor so as to separate a high-pressure space and a low-pressure space and includes: a plurality of thin plates arranged along an outer peripheral surface of the rotor. Each of the thin plates has a thin-plate tip surface facing the outer peripheral surface of the rotor; a first side plate disposed so as to face the high-pressure space and covering outer peripheral regions of first side surfaces; and a second side plate disposed so as to face the low-pressure space and covering outer peripheral regions of second side surfaces. The first side surface of each of the thin plates is covered with the first side plate in a region extending further to an inner side, in a radial direction of the rotor, than a region of the second side surface covered with the second side plate.