A washing machine including a tub, a spin basket rotatably mounted in the tub, a pulsator rotatably mounted in the spin basket and having a pulsator hub part extending downward from a center portion of the pulsator, a driving device to generate rotational force, a wash shaft to transmit the rotational force generated from the driving device to the pulsator, and a buoyancy clutch upwardly and downwardly movably mounted to the pulsator hub part and configured to move up and down by buoyancy. The buoyancy clutch is configured to rotate together with the pulsator. When the buoyancy clutch moves down, the spin basket is engaged with the buoyancy clutch and receives the rotational force.