A sealing device for a steam turbine which includes a rotating region formed by a rotor and a first member constructed to rotate integrally with the rotor, and a fixed region formed by a casing containing the rotating region, and by a second member fixed to the casing, the sealing device being built into the steam turbine, the sealing device comprising: sealing fins provided in both or either of the rotating region and the fixed region; the sealing device further comprises spacers provided on the rotating region or fixed region, both facing the sealing fins, the spacers each using a free-cutting metal, characterized In that the fixed region includes a movable region that is movable in the axial direction of the rotor by a pressure action of steam circulating through the steam turbine, the movable region being constructed to move when urged by urging means acting in a direction opposite to that of the pressure action of the steam; and when a loading pressure that the steam applies to move the movable region In the axial direction of the rotor is smaller than an urging force that the urging means uses to urge the movable region in the opposite direction, the sealing fin and spacer that face each other are ready to come into contact with each other; and upon the loading pressure exceeding the urging force, the movable region moves to a position at which a clearance between the sealing fin and spacer that face each other reaches a preset value, wherein when the sealing fins are disposed on the fixed region the sealing fins are mounted on the movable region so that each of the sealing fins is disposed to move in an axial direction of the rotor with respect to the rotating region; and when the spacers are disposed on the fixed region the spacers are mounted on the movable region so that each of the spacers is disposed to move in the axial direction of the rotor with respect to the rotating region. sealing fins provided in both or either of the rotating region and the fixed region; the sealing device further comprises spacers provided on the rotating region or fixed region, both facing the sealing fins, the spacers each using a free-cutting metal, characterized In that characterized In that when a loading pressure that the steam applies to move the movable region In the axial direction of the rotor is smaller than an urging force that the urging means uses to urge the movable region in the opposite direction, the sealing fin and spacer that face each other are ready to come into contact with each other; and upon the loading pressure exceeding the urging force, the movable region moves to a position at which a clearance between the sealing fin and spacer that face each other reaches a preset value, wherein when the sealing fins are disposed on the fixed region the sealing fins are mounted on the movable region so that each of the sealing fins is disposed to move in an axial direction of the rotor with respect to the rotating region; and when the spacers are disposed on the fixed region the spacers are mounted on the movable region so that each of the spacers is disposed to move in the axial direction of the rotor with respect to the rotating region. upon the loading pressure exceeding the urging force, the movable region moves to a position at which a clearance between the sealing fin and spacer that face each other reaches a preset value, wherein when the sealing fins are disposed on the fixed region the sealing fins are mounted on the movable region so that each of the sealing fins is disposed to move in an axial direction of the rotor with respect to the rotating region; and when the spacers are disposed on the fixed region the spacers are mounted on the movable region so that each of the spacers is disposed to move in the axial direction of the rotor with respect to the rotating region.