A light guide device is used in a back light module that more uniformly mixes different colored light emitted from a plurality of LEDs and transfers the mixed light to a display panel, wherein a light loss can be minimized during the light mixing process and the light can be more uniformly mixed. A light guide device is disclosed for mixing different colored light emitted from a plurality of light emitting diodes (LEDs) and guiding the mixed light to a display panel, wherein the light guide device comprises a light guide portion in the form of a plate arranged at a rear of the display panel; and a light mixing portion formed integrally with the light guide portion and including a light incidence surface adjacent to the plurality of LEDs and a light mixing area for mixing the light with difference colors incident through the light incidence surface.