LEVEL GAGE

PROBLEM TO BE SOLVED: To provide a level gage, by an optical method, which is installed at the side face of a liquid tank, which is used also as a window fox level monitoring and which can be mass-produced at low costs. SOLUTION: In the level gage, the surface of a liquid is observed visually, and a signal is transmitted according to whether the level of the surface of the liquid is higher or lower with reference to a definite position. The level gage is composed of a transparent block body which is to be attached to the outer surface of the liquid tank. A recessed part which is to be connected to a hole formed in the liquid tank is formed at the block body. A protrusion whose tip part is prism-shaped is installed from the face of the recessed part. A light emitting element which is directed to one out of both slopes of the protrusion whose tip part is prism-shaped and a light receiving element which is directed to the other are installed at the outside of the block body, The signal is transmitted according to whether the light receiving element receives light or not.