In this paper , we report the discovery of a binary composed of a brown dwarf and a low-mass M dwarf from the observation of the microlensing event OGLE-2014-BLG-0257 . Resolution of the very short-lasting caustic crossing combined with the detection of subtle continuous deviation in the lensing light curve induced by the Earth ’ s orbital motion enable us to precisely measure both the Einstein radius \theta _ { E } and the lens parallax \pi _ { E } , which are the two quantities needed to unambiguously determine the mass and distance to the lens . It is found that the companion is a substellar brown dwarf with a mass 0.036 \pm 0.005 M _ { \odot } ( 37.7 \pm 5.2 M _ { J } ) and it is orbiting an M dwarf with a mass 0.19 \pm 0.02 M _ { \odot } . The binary is located at a distance 1.25 \pm 0.13 kpc toward the Galactic bulge and the projected separation between the binary components is 0.61 \pm 0.07 AU . The separation scaled by the mass of the host is 3.2 { AU } / M _ { \odot } . Under the assumption that separations scale with masses , then , the discovered brown dwarf is located in the zone of the brown dwarf desert . With the increasing sample of brown dwarfs existing in various environments , microlensing will provide a powerful probe of brown dwarfs in the Galaxy .