To provide a pump having a high circulation efficiency instead of its small capacity and extremely simplified structure for allowing to manufacture the pump at a low cost and capable of coping with lake purification because of its excellent cost effectiveness.

A rotor capable of revolving around a vertical shaft is positioned at a water surface so that a part of it sticks out of the water and a part of it is down in the water. The rotor is pivoted above the water surface and has a vertical passage with a downward opening below the water surface and slanting passages for branched from the vertical passage below the water surface. The slanting passages have water passages in a simple shape which are connected to sprinkling ports above the water surface. Basic structure is a circulation pump without a case which can be manufactured at a very low cost. The caseless pump includes rotor revolution mechanism with a windmill and sprinkle tubes increased in angles of the slating passages.