PURPOSE: To correctly detect water level without exposing a detection element of a liquid detection sensor outside.

CONSTITUTION: Detection elements 1 are so constituted that a pair of electrodes are placed near each other on approximately the same plane. The detection elements 1 is connected to a detection circuit, and the detection circuit judges presence of liquid by detecting capacity changes between electrodes that follows approach of the liquid. The detection elements 1 is buried in the peripheral wall of a bath tub 3, and when water level approaches near the detection elements 1, the capacitance between both electrodes changes, for detection signal to be generated by the detection circuit, and open/close of a tap 4 is controlled.