A backlight unit includes: a lower case including a bottom portion and a side portion on an edge of the bottom portion, a light guide plate accommodated in the lower case, and a light source module including a circuit board between the light guide plate and the side portion of the lower case and a light source on the circuit board, where the light guide plate includes a first light collecting pattern on a lower surface of the light guide plate, and a second light collecting pattern on the lower surface of the light guide plate and between the light source module and the first light collecting pattern.