To provide a simple metering tank capable of measuring a constant amount of water, and supplying the water into a mixer or the like for materials to be kneaded containing cement as a base material.

A liquid supplied to a tank 1 is set in a manner that the liquid can be taken out of the tank 1 to its outside by a discharge pipe 2; a supply pipe 4 in an inverted U shape movable vertically is installed in the upper part of the tank 1; at an appropriate spot of a hanging part 4a of this supply pipe 4, a liquid level sensor 5 for stopping liquid supply from the supply pipe 4 by detection is provided, and a liquid drain hole 6 is formed below this liquid level sensor 5; and a pump P is installed so that its delivery part 4d connected to a rising part 4c of the supply pipe 4 becomes below the liquid drain hole 6 in the hanging part 4a of the supply pipe 4.