PURPOSE: To detect the water level of a washing tank with simple configuration without providing an air hose by detecting a resistance value between electrodes provided on the both sides of a pressure detection body by utilizing a change in the resistance value of a pressure sensitive conductive rubber caused by the pressure of water in the washing tank.

CONSTITUTION: A pressure detection body 23 is composed of a pressure sensitive conductive rubber 20, for which the resistance value in a thickness direction is changed according to the amount of distortion in the thickness direction, and electrodes 21 and 22 arranged on the both sides of the pressure sensitive conductive rubber 20 by a suitable adhering means. When the water is fed into a washing tank 1 and the water level is made higher than an opening part 9, the water pressure is impressed to a seal member 25 and the pressure sensitive conductive rubber 20 is compressed in the thickness direction. Generally, the pressure sensitive conductive rubber 30 is equipped with a character that the resistance value is lowered when it is compressed, and accordingly, the more the water pressure is increased, the more the resistance value between terminals 26 and 27 is reduced. Since the resistance value is widely changed together with the water level, the water level can be detected with high accuracy.