Panasonic EZ-10 sensor can be hosed down because of its IP67 construction and the non-corrosive stainless steel sensor mounting bracket. As the penetrating power is strong, its beam can pass through not only translucent containers (PFA tanks, etc.) but also opaque containers of shampoo bottles, etc., and the sensor can reliably detect the liquid inside. It is possible to set its sensitivity adjuster so that water drops, bubbles in the water, or froth on the water surface are not detected. Several sensors can be mounted adjacently by fitting optional slit masks. Further, they can detect the liquid level accurately. Plug-in connector type which enables connection / disconnection of the cable by one-touch is available. Anyone can easily replace the sensor in a minute. Light-ON or Dark-ON operation can be selected. The output operation can be changed easily.