PURPOSE: To effectively control the wave rising on the water surface of a live well and preserve the fish in the live well for a number of hours without weakening it by setting up an almost plate-shaped live well float which covers the water surface of the live well.

CONSTITUTION: The suction port 19 and the drainage port 20 are provided at the bottom of the live well 18, i.e. ship's bottom 8a. The suction port 19 is opened at the slope 22 on the stern of the concave 21 which is formed at the ship's bottom 8a. The suction and drainage ports 19 and 20 are provided with the cap which controls the water flow in the live well 18 on the external surface of the projection on the live well 18. The float 31 floats so as to cover the water surface of the live well and has the window 32 so that caught fish can easily be thrown into the live well 18. Consequently, when the hull 8 rolls and pitches, the live well 18 also does at the same time. However, the wave rising on the water surface is controlled by the float 31 and shade is always provided under the float, thereby reducing the damage of the fish.