A washing machine includes a wobbling device having a rotary blade. The wobbling device causes a wobbling action of a washboard without rotating the washboard during a washing mode operation, and rotates the rotary blade in one direction to allow a sufficient amount of wash water to flow upward through an ascending water current guide and fall from an upper portion of a spin-drying tub onto clothes contained in the spin-drying tub, thus effectively washing the clothes. The washboard is installed at a lower portion in the spin-drying tub such that it wobbles upward and downward. The rotary blade is installed under the washboard, and is rotated in one direction by torque of a washing shaft. The rotary blade is fitted over a boss which couples a vertical rotary shaft of the wobbling device to the washing shaft, and is rotated by the torque of the washing shaft. The water current guide extends along a sidewall of the spin-drying tub from a lower end to an upper end of the spin-drying tub. Water currents generated from the rotary blade are guided to the upper portion of the spin-drying tub and fall from the upper portion to the lower portion of the spin-drying tub.