To provide a processing ship for lake water quality purification improvement equipped with a lake water quality purification improving device of simple structure, attaining easy and efficient operation.

A balloon station 20 which is installed on a ship, and stores and arranges a plurality of spherical balloons 10 formed out of thin-walled steel sheet or synthetic resin material whose outer surface is coated with adsorbing material with its inside filled with air, a balloon pressing means 40 which discharges many balloons sequentially and continuously into water passing through a balloon guiding conduit 30, and a balloon recovery means 50 which leads the discharged balloons to the balloon station sequentially are disposed, and a cleaning means 60 which cleans the recovered balloons is provided in this lake water quality purification improving device. The balloon recovery means is constituted of a tubular guide vane 52 made of steel or reinforced plastic which is formed protruding from the lake bottom toward above the water so as to move freely by a support protruding from the ship body, a fishing net 54 or a thin-walled pored plate, and a balloon recovery device which transfers the balloons sequentially to the balloon station.