A washing machine includes a cabinet; an outer basket in the cabinet and configured to contain wash water; an inner basket in the outer basket and configured to accommodate laundry; a water supply valve unit in the cabinet and connected to an external water supply source to receive wash water; a cabinet cover on an upper side of the cabinet and having an input hole for the laundry; and a micro-bubble generator configured to receive wash water from the water supply valve unit, generate micro-bubbles, and supply the micro-bubbles to a washing space. The micro-bubble generator includes a nozzle unit at or near the input hole and configured to generate micro-bubbles by receive wash water in which gas is dissolved or mixed and discharge wash water having the micro-bubbles therein into the inner basket after the micro-bubbles are generated.