PURPOSE: To provide a water level sensor in which a water level sensing can be easily and optionally changed.

CONSTITUTION: The sensor is provided with a surge prevention tube 1 provided in a water tank A, a resistor band 2 provided on the side face of the surge prevention tube 1, a conductor 3 provided on the side face of the surge prevention tube 1 opposed to the resistance band 2, a float 4 floated on the water surface in the surge prevention tube 1, a conduction link rod 6 built in the float 4, and a control panel 7 sensing a water level (h) in the water tank A based on a current I flowing to a water level detection circuit B comprising the resistor band 2, the conduction link rod 6 and the conductor 3.