PURPOSE: To indicate the waterlevel of the title vessel by illuminating water in a transparent water pipe which forms part of a water condit communicating with the lower part of the vessel and to make it possible that the waterlevel is indicated well visibly by a cheap formation.

CONSTITUTION: A water conduit 21 wherein the upper part of a vessel 20 communicates with the lower part thereof, is composed of a transparent water pipe 22, an illuminating part 25 and so on. At the lower part of the illuminating part 25 transparent, an electric lamp 26 is provided upward and is connected to an illuminating means 27. The electric lamp 26 is driven by the illuminating means 27. Light emitted upward through the illuminating part 25 illuminates water in the transparent water pipe 22. Since the optical axis of the light emitted by the electric lamp 26 is almost perpendicular to a water surface, the light is reflected at the water surface and in the water pipe 22, only the part filled with the water is lightened. Therefore, when the title vessel main body is watched at its front, a waterlevel can be found since the water pipe 22 can be seen through a water-measuring window and only the part filled with the water comes to the front brightly. In addition, since the indication of this waterlevel illuminates the water in the water pipe 22, it is accurate and can be visually recognized even from far away well enough.