PURPOSE: To use titled sensor even the liquid having bigger viscosity by deforming the partitioned chamber composed of bellows, etc. according to the height of the liquid level of the inside of a tank and by providing a shielding plate body shielding a light when the liquid level is raised.

CONSTITUTION: The cylinder part of a partition chamber 1 is made of a bellows, etc., 1a and telescopically, and a float 1b is provided at the lower part. An emission part 2, photodetecting part 3 and control part 4 are also provided on the upper part and a glass fiber 5 is extended from the emission part 2 and photodetecting part 3 and the tip part thereof is opposed. A shielding body 6 is provided under the opposing glass fiber thereof. When the partition chamber 1 is dipped into the liquid 10, then, the bellows 1a is contracted, the shielding body 6 enters between the tip part of the optical fiber 5 to shield the light, which does not reach the detecting part 3. Since the light shielding body is provided inside the partition chamber deforming according to the height of the liquid level the liquid level of even the liquid having bigger viscosity can be detected with high accuracy.