To provide a level gauge, level, manometer, and thermometer using it, which do not depending on the refractive index of measuring target liquid, capable of measuring the liquid level not discretely but continuously.

The liquid level gauge is constituted of: an optical fiber sensor 9 spliced with a sensor part 4 of a hetero-core part 30 being mode regulation releasing part at its tip part; a light source 1 for light emitting into the core of the optical fiber sensor 9; a signal detector 6 being the direct intensity of returned light to the light source 1 while receiving mutual action with external at the sensor part 4. By measuring the intensity of returned light from the tip of the sensor part 4, at least a part of which is dipped into the measurement objective liquid LQ, the liquid level LS of the objective liquid LQ is measured.