PURPOSE: To improve the operating state of a pump, to increase the saving of energy, to simplify the programming of the automatic control of water supply, to reduce the cost, to increase the reliability of a water supply system, and to prevent the deterioration and pollution of water for fire, by sufficiently solving the problem of the control of a water surface generated in a water tank set at a high place.

CONSTITUTION: This device is provided with a highest water level control mechanism 1 (GSK), a controllable water level control mechanism 3 (TSK), and an extinguishing water level control mechanism 5 (XSK). Those three mechanisms are connected in series with upper and lower water level difference pipes 2 and 4 so that a valve device combined like a cylinder can be constituted. This valve device is positioned along a shaft between an entrance and an outflow pipe, and the automatic control of three water surfaces H1, H2, and H3 is attained.