A steam turbine includes: a rotor shaft including a shaft core that rotates about an axis and disk portions that are fixed to the shaft core and expand toward a radially outer side in the shaft core; and a plurality of rotor blades that are fixed to outer peripheries of the disk portions and are disposed in a circumferential direction of the shaft core. A first surface that is toward a first direction including a directional component toward a radially inner side of the shaft core is formed on each of the rotor blades, and a second surface that is toward a second direction including a directional component toward the radially outer side and faces the first surface is formed on each of the disk portions.