To eliminate influence of fluctuation in a liquid temperature and specific gravity resulting in an error of a level measurement value for improving measurement precision in a sensor measuring a level by converting a fluid pressure into deflection of an optical fiber.

This level sensor is provided with a pressure detection part 1 transmitting displacement by a fluid pressure in bellows 11 to a movable shaft 12 so that deflection matching the fluid pressure is generated in the optical fiber 5a having an FBG element between rollers 13 and 14, a specific gravity detection part 2 generating deflection in the optical fiber 5b having the FBG element between rollers 24 and 25 in accordance to a difference of pressures working on bellows 21 and 22 arranged face to face, and a temperature detection part 3 generating deflection matching a temperature in the optical fiber 5b between the rollers 24 and 31. By this level sensor, temperature correction and specific gravity correction of a fluid level measurement value can be carried out.