Disclosed is a washing machine comprising a main drum rotatably mounted in the tub, a sub drum mounted inside the main drum to be relatively rotatable with respect to the main drum, an outer shaft for rotating the main drum, an inner shaft for rotating the sub drum and disposed inside the outer shaft, and a driving motor. The driving means is configured to rotate the main drum and the sub drum in different directions and/or with different rotational speeds. The washing machine further comprises a main drum spider to connect the main drum to the outer shaft to transfer a driving force of the driving means to the main drum, and a sub drum spider to connect the sub drum to the inner shaft to transfer a driving force of the driving means to the sub drum, wherein the two spiders are arranged to be independently rotatable.