A turbine includes a blade, a structure installed at a tip section side of the blade via a gap and configured to relatively rotate with respect to the blade, a step section formed at the tip section of the blade, having at least one step surface, and protruding toward a portion opposite to the tip section of the structure, a seal fin formed at the portion opposite to the tip section of the structure, extending toward the step section, and configured to form a micro gap between the step section and the seal fin, and a cutout section formed at the step surface to be connected to an upper surface of the step section. The cutout section guides a separation vortex separated from a main stream of a fluid passing through the gap toward the seal fin on the upper surface of the step section.