We claim:
1. A turbine comprising:
a blade (50) disposed on a shaft body (30) around a rotary axis wherein a tip shroud (51) extending in a circumferential direction is installed at a tip section of the blade (50);
a structure (11) configured to surround the blade (50) and installed at a tip section side of the blade (50);
at least two step sections (52) formed at one of the tip shroud (51) of the blade (50) and a section of the structure (11) opposite to the tip shroud (51) and protruding toward the other of the tip shroud (51) of the blade (50) and the section of the structure (11) opposite of the tip shroud (51), the step sections (52) having step surfaces (53A,53B,53C) and upper surfaces (152A, 152B, 152C); and
at least two seal fins (15), corresponding to the at least two step sections (52), respectively, the at least two seal fins (15) being formed at the other of the tip shroud (51) of the blade and the section of the structure (11) opposite to the tip shroud (51), extending toward the step sections (52) respectively, and configured to form a respective gap (H) between the corresponding step sections (52) and the seal fins (15);
wherein protruding heights of the step sections (52) are gradually increased from an upstream side toward a downstream side,
inclined sections are formed at each of the step surfaces (53A,53B,53C), the inclined sections being inclined from the upstream side toward the downstream side, and
the inclined sections comprises upper edge sections (55) that are respectively connected to the adjacent upper surface (152A,152B,152C),
an inclination angle of each inclined section with respect to a radial direction of the rotary axis is set to be larger for the inclined section formed at the step surface located in the downstream side.
2. A turbine comprising:
a blade (50) disposed on a shaft body (30) around a rotary axis wherein a tip shroud (51) extending in a circumferential direction is installed at a tip section of the blade (50);
a structure (11) configured to surround the blade (50) and installed at a tip section side of the blade (50);
at least two step sections (52) formed at one of the tip shroud (51) of the blade (50) and a section of the structure (11) opposite to the tip shroud (51) and protruding toward the other of the tip

shroud (51) of the blade (50) and the section of the structure (11) opposite of the tip shroud (51), the step sections (52), having step surfaces (53A,53B,53C) and upper surfaces (152A,152B, 152C); and
at least two seal fins (15), corresponding to the at least two step sections (52), respectively, the at least two seal fins (15) being formed at the other of the tip shroud (51) of the blade (50) and the section of the structure (11) opposite to the tip shroud (51), extending toward the step sections (52) respectively, and configured to form a respective gap (H) between the corresponding step sections (52) and the seal fins (15);
wherein protruding heights of the step sections (52) are gradually increased from an upstream side toward a downstream side,
arc-shaped sections are formed at each of the step surfaces (53A,53B,53C) and smoothly connected to the respective adjacent upper surfaces (152A,152B,152C) , and
an angle between a tangential direction of a portion of the arc-shaped section connected to the
respective adjacent upper surface (152A,152B,152C) and a radial direction of the rotary axis is set to
be larger for the arc-shaped section formed at the step surface located in the downstream side.
3. A turbine comprising:
a blade (40) wherein a hub shroud (41) extending in a circumferential direction is installed at a tip section of the blade (40);
a shaft body (30) configured to rotate around a rotary axis, installed at a tip section side of the blade (40);
at least two step sections (52) formed at one of the hub shroud (41) of the blade (40) and a section of the shaft body (30) opposite to the hub shroud (41) and protruding toward the other of the hub shroud (41) of the blade (40) and the section of the shaft body (30) opposite of the hub shroud (41), the step sections (52) having step surfaces (53A,53B,53C) and upper surfaces (152A,152B,152C); and
at least two seal fins (15), corresponding to the at least two step sections (52), respectively, the at least two seal fins (15) being formed at the other of the hub shroud (41) of the blade (40) and the section of the shaft body (30) opposite to the hub shroud (41), extending toward the step sections (52) respectively, and configured to form a respective gap (H) between the corresponding step sections (52) and the seal fins (15);
wherein protruding heights of the step sections (52) are gradually increased from an upstream side toward a downstream side,
inclined sections are formed at each of the step surfaces (53A,53B,53C), the inclined sections being inclined from the upstream side toward the downstream side, and
the inclined sections comprises upper edge sections (55) that are respectively connected to the adjacent upper surface (152A,152B,152C),
an inclination angle of each inclined section with respect to a radial direction of the rotary axis is set to be larger for the inclined section formed at the step surface located in the downstream side.

4. A turbine comprising:
a blade (40) wherein a hub shroud (41) extending in a circumferential direction is installed at a tip section of the blade (40);
a shaft body (30) configured to rotate around a rotary axis, installed at a tip section side of the blade (40);
at least two step sections (52) formed at one of the hub shroud (41) of the blade (40) and a section of the shaft body (30) opposite to the hub shroud (41) and protruding toward the other of the hub shroud (41) of the blade (40) and the section of the shaft body (30) opposite of the hub shroud (41), the step sections (52) having step surfaces (53A,53B,53C) and upper surfaces (152A,152B,152C); and
at least two seal fins (15), corresponding to the at least two step sections (52), respectively, the at least two seal fins (15) being formed at the other of the hub shroud (41) of the blade (40) and the section of the shaft body (30) opposite to the hub shroud (41), extending toward the step sections (52) respectively, and configured to form a respective gap (H) between the corresponding step sections (52) and the seal fins (15);
wherein protruding heights of the step sections (52) are gradually increased from an upstream side toward a downstream side,
arc-shaped sections are formed at each of the step surfaces (53A,53B,53C) and smoothly connected to the respective adjacent upper surfaces (152A,152B,152C), and
an angle between a tangential direction of a portion of the arc-shaped section connected to the respective adjacent upper surface (152A,152B,152C) and a radial direction of the rotary axis is set to be larger for the arc-shaped section formed at the step surface located in the downstream side.