An inner drum of a washing machine has a plurality of hollow lifting ribs arranged on the side wall of the drum that communicate with the interior of the drum. At least one drainage port communicating with the hollow portions of the lifting ribs is formed in the side wall of the drum. A sealing valve is located inside each lifting rib at each drainage port. During high-speed rotation of the drum, valve bodies of the sealing valves move along a radial center direction of the drum under a centrifugal force, to open the drainage ports. Through this arrangement, discharging water flow in the drum to the outside from the hidden drainage ports is achieved. Meanwhile, centrifugal force during the high-speed rotation of the drum is used to control valve cores of the sealing valves such that the drainage ports are automatically opened for drainage from the drum.