To easily change a set water level by providing many lead wires embedded in a vertical direction inside the panel unit of the wall surface of a water tank for which electrode terminal surfaces are exposed with a prescribed height interval and a terminal part for connecting the respective lead wires to a control panel side.
Upper and lower electrode panel units 18 and 20 for constituting a liquid level detector are incorporated at the almost center part of respective side face panel units 12 and 14. For the electrode panel units 18 and 20, many lead wires are parallelly embedded along the vertical direction and rivet-like electrodes 24 connected to the lower ends of the respective lead wires are exposed in the equal intervals in the vertical direction. The upper ends of the respective lead wires are projected to the upper flanges of the electrode panel units 18 and 20 and projected parts are respectively connected through the lead wire 4 for connection to a control panel 5 as the terminal part. Then, by respectively switching the respective lead wires or changing the connection corresponding to a lowest water level and a highest water level to be obtained, the set water level is changed.