A new fiber-optic sensor system consisting of a fiber Bragg grating (FBG) cantilever as a transducer is proposed and demonstrated to realize simultaneous measurement of magnitude and direction of deflection. For the FBG mounted on a stainless steel cantilever, a change in the bending deflection gives rise to a monotonous shift in the Bragg resonance wavelength of the grating while the deflection direction results in either a red- or blue-shift in the Bragg wavelength due to a stretched or shrunk state of the grating. As an application of this deflection sensor, the water flow rate was measured, which showed good agreement with the theoretical analysis.