PURPOSE: To enable generation of bubbles to be inhibited in damping water to be supplied into a water vessel without use of defoaming agent by providing a flow regulation valve in a guide channel for in-tank wetting water into a damping water return conduit pipe.

CONSTITUTION: A feeder conduit pipe 6 branches out at a position where it is immersed in damping water of a tank 2, and this branched conduit pipe 7 connects with a return conduit pipe 10 halfway, extending into the tank 2. The return damping water in the return conduit pipe 10 is returned into the tank 2. An ejector 12 is provided in a connection of the return conduit pipe 10 to the branched conduit pipe 7, forcibly sucking the return damping water from the return conduit pipe 10 into the tank 2. A flow regulation valve 7A is provided on the branched conduit pipe 7, regulating a flow to be injected from an orifice 12A. In this way, a negative pressure generated on an ejector 12 is controlled to regulate the return quantity of damping water through the return conduit pipe 10. Thus it is possible to inhibit generation of bubbles in damping water without use of defoaming agent under a simple structure.