The present invention relates to a washing machine comprising an outer tub containing water, and an inner tub disposed in the outer tub to accommodate laundry and rotated about a horizontal axis. The washing machine includes: a motor for providing rotational force; an outer shaft that has a first hollow, and rotates the inner tub; an inner shaft disposed in the first hollow and rotated by the motor; a pulsator disposed in the inner tub and coupled with the inner shaft; a planetary gear train for transmitting rotational force of the motor; a carrier mover which has an outer circumferential surface that is spline-coupled to an inner circumferential surface of the outer shaft, and an inner circumferential surface that is screwed with an outer circumferential surface of the clutch carrier; and a stopper restricting movement of the carrier mover, thereby achieving various washing modes with a simple mechanism by rotating the inner tub and the pulsator.