PURPOSE: To facilitate the checking of a set value of a leakage detection level under an installation by providing a working point position display window and a graduation on a frame base while a working point position display indicator is provided at a fixed section of a level detecting section.

CONSTITUTION: A level detecting section 10 is mounted on a keep plate 7 for fixing a detecting section fixing plate 5. A working point position indicator 13 is mounted on the fixing plate 5, which is clamped on a stationary type frame base 4 with a fixing screw 12. The checking of a detection level of a leaked water within a sump pit equipped with this apparatus can be made easily by watching a pointer 13 and a working point display set level graduation of a working point display window on the frame base 4 with the apparatus left in the sump pit. This also allows always keeping of a working point of an electrode type level detecting section 10 and a working point set level graduation constant thereby facilitating the setting of a level.