Abstract: Disclosed is a washing machine which can strongly pump a washing liquid towards an upper portion of a spin tub while a washing cycle is being executed. The washing machine has a housing and an outer tub disposed in the housing so as to receive the washing liquid. A spin tub accommodated in the outer tub is divided into an upper chamber and a lower chamber by a compartment, and is formed at an inner wall thereof with first and second cylinders which are positioned in opposition to each other. The washing machine has a motor for generating a rotational force, a pulsator mounted on an upper surface of the compartment, and a pulsator driving section for driving the pulsator by receiving the rotational force from the motor. First and second piston assemblies are respectively disposed within the first and second cylinders in order to pump the washing liquid towards an upper portion of the spin tub.