A steam turbine rotor blade comprising: a blade body which includes a pressure-side surface and a suction-side surface extending in a blade height direction (Dh) and a leading edge portion which is formed by the pressure-side surface and the suction-side surface and extends in the blade height direction (Dh); a protrusion portion which is provided on a tip end portion of the blade body in the blade height direction (Dh) and protrudes from the suction-side surface toward the leading edge portion side; and a transition-region seal member which is provided so as to cover at least a portion of a base end-side surface of the protrusion portion facing a base end side opposite to a tip end in the blade height direction (Dh), and a leading edge-side transition region, facing the leading edge portion side, of a connection portion between the protrusion portion and the suction-side surface, wherein a first recessed portion (613, 613A) which is recessed from the suction-side surface is formed in the leading edge-side transition region, and wherein the transition-region seal member includes a front-side seal portion which is disposed in the first recessed portion (613, 613A) such that a surface of the front-side seal portion is flush with a surface of the blade body; characterized in that the transition-region seal member is formed of a material having a hardness higher than that of the blade body; and the transition-region seal member further includes a base end-side seal portion which is integrally formed with the front-side seal portion and is disposed on the base end-side surface such that a surface of the base end-side seal portion protrudes from the base end-side surface. a blade body which includes a pressure-side surface and a suction-side surface extending in a blade height direction (Dh) and a leading edge portion which is formed by the pressure-side surface and the suction-side surface and extends in the blade height direction (Dh); a protrusion portion which is provided on a tip end portion of the blade body in the blade height direction (Dh) and protrudes from the suction-side surface toward the leading edge portion side; and a transition-region seal member which is provided so as to cover at least a portion of a base end-side surface of the protrusion portion facing a base end side opposite to a tip end in the blade height direction (Dh), and a leading edge-side transition region, facing the leading edge portion side, of a connection portion between the protrusion portion and the suction-side surface, wherein a first recessed portion (613, 613A) which is recessed from the suction-side surface is formed in the leading edge-side transition region, and wherein the transition-region seal member includes a front-side seal portion which is disposed in the first recessed portion (613, 613A) such that a surface of the front-side seal portion is flush with a surface of the blade body; characterized in that the transition-region seal member is formed of a material having a hardness higher than that of the blade body; and the transition-region seal member further includes a base end-side seal portion which is integrally formed with the front-side seal portion and is disposed on the base end-side surface such that a surface of the base end-side seal portion protrudes from the base end-side surface.