A washing machine includes an alternating current (AC) motor which generates torque, a clutch assembly which selectively transfers the torque to a rotating tub and a pulsator, a speed detector which detects a rotary speed of the clutch assembly, and a controller configured to repetitively perform operating and stopping the operating of the AC motor based on a predetermined target speed and the rotary speed of the clutch assembly in a spin-drying operation. The controller gradually increases the torque of the AC motor while operating the AC motor.