The present invention provides a light guide plate which can process in polarization separation, and emit a light in a desirable direction, a surface light source device, and a liquid crystal display device. A light guide plate 30 includes a light guide plate main body 31 including a first surface 31a on which a light 100 output from a light source section 20 is made incident, a second surface 31b adjacent to the first surface, a third surface 31d which faces the first surface, and is adjacent to the second surface, and a fourth surface which faces the second surface, and is adjacent to the third surface, and a diffraction grating section 32 arranged on the second surface 31b wherein; the diffraction grating section 32 is configured in such a way that a plurality of gratings 33 consisting of a dielectric is arranged in parallel at an interval Λ along a predetermined direction facing from the first surface to the third surface, wherein; when a wavelength of a visible region possessed by a light 100 is set to be λ, the interval Λ satisfies 1≧Λ/λ≧0.5, and when a refractive index of the light guide plate main body 31 is set to be ns, and a refractive index of the grating 33 is set to be ng, the refractive index ng satisfies ng-ns≧0.15.