A compact washing machine capable of improving detergency or reducing a washing time is provided. A drum 30 may be rotatably installed in a tub 20 installed in the inside of a housing 10 in the state in which an opening 12 is toward an opening of the drum 30. A pulsator 40 having a protrusion 45 extending in a radial direction may be rotatably installed on a bottom of the drum 30. During washing operation, a controller 60 may control a driving device 50 to rotate the pulsator 40 and the drum 30 in opposite directions.