To provide a plane surface lighting device that can raise use efficiency of light emitted from a light source while thinning the plane surface lighting device.
The plane surface lighting device includes a light source 100, a light guide plate 200 having a light incident end face 212 for entering light emitted from the light source 100 and a light emitting surface 224 for emitting light incident from the light incident end face 212, and a diffractive optical element 230 arranged between the light source 100 and the light incident end face 212. The light guide plate 200 has an inclined part 210 arranged on a light incident end face 212 side and preparing an inclined surface 214 to gradually increase its thickness toward the light incident end face 212, and the diffractive optical element 230 makes light emitted from the light source 100 deflect in an inclination direction of the inclined surface 214 as a whole.
MIYAMOTO MASAO
KITAMURA ATSUSHI
