A rotor blade attached to a rotor shaft rotatable around an axis includes: a blade body extending in a radial direction with respect to the axis and having a blade-shaped cross section orthogonal to the radial direction; a shroud provided at an end of the blade body on a radial outer side, and a seal fin protruding from the shroud toward an outer circumferential side, and the seal fin includes: a seal fin body extending in a plate shape in a circumferential direction; and a reinforcing portion provided on at least one plate surface of the seal fin body to increase a thickness of the seal fin, the reinforcing portion gradually increasing in dimension in the radial direction toward the center in the circumferential direction.