An optical fiber sensor that can detect a liquid level or detect a
property of liquid with high reliability even under a frequently
vibrational environment. The optical fiber sensor includes an optical
fiber that includes a core having an area where a grating is formed and a
clad, the optical fiber being disposed so that at least a part of the
area with the grating is immersed in liquid, a light source for making
light incident to the optical fiber so that a cladding mode light having
a wavelength band is generated by the grating, and a light receiving unit
for detecting the intensity of light which is incident from the light
source to the optical fiber and transmitted through the grating.