Dissolving a solid detergent packed in a detergent container while forming a dissolved surface into a horizontal surface without leaving any detergent in the container. Among these, a rotary nozzle within a closed structure, in which the rotary-nozzle fixture is mounted in a center of rotation of a rotary-nozzle body, the rotary-nozzle body is formed to be substantially S-Shaped in a plan view and divided vertically into two upper and lower parts, where the lower part of the rotary-nozzle body is provided with a rotating shaft hole, which is disposed centrally in a longitudinal direction, formed on a top thereof with a circular groove.