A steam turbine includes a casing, a rotor arranged inside the casing so as to extend in an axial direction of the casing, a rotor disk integrally formed with the rotor, a rotor-side implanting portion formed in the rotor disk, a plurality of moving blades arranged on the rotor disk in a circumferential direction of the rotor, and a moving blade-side implanting portion formed in the moving blade, in which the moving blade-side implanting portions of the moving blades are engaged with the rotor-side implanting portions, respectively. A cooling medium flows through a gap formed at least on a blade portion side of the moving blade among gaps formed between the moving blade-side implanting portions and the rotor-side implanting portions.