A backlight unit comprising: a first reflector; a second reflector; at least one light source disposed between the first reflector and the second reflector, an optical member spaced by a predetermined distance from the second reflector, wherein an air guide is defined between the second reflector and the optical member, wherein the second reflector comprises a specular reflection area and a diffuse reflection area, and wherein the specular reflection area occupies 5 to 50% of an entire area of the second reflector, characterized in that the second reflector comprises an inclined surface including a plurality of inclined surfaces having at least two inflection points, and concave lines and convex lines are alternately arranged along the inclined surface of the second reflector, the diffuse reflection area comprises first and second diffuse reflection areas (300b1, 300b2), configured so as to reflect incident light in a Lambertian distribution and/or a Gaussian distribution, an incidence angle of light incident upon each point of the first diffuse reflection area (300b1) is 55 degrees or more with respect to a normal line passing each point, an incidence angle of light incident upon each point of the second diffuse reflection area (300b2) is 60 degrees or more with respect to a normal line passing each point, a distance between the specular reflection area and the light source is less than that between the first diffuse reflection area and the light source, a distance between the first diffuse reflection area and the light source is less than that between the second diffuse reflection area (300b2) and the light source, and the first diffuse reflection area (300b1) is configured so that a quantity of light reflected in the Gaussian distribution is greater than a quantity of light reflected in the Lambertian distribution, and the second diffuse reflection area (300b2) is configured so that a quantity of light reflected in the Lambertian distribution is greater than a quantity of light reflected in the Gaussian distribution. a first reflector; a second reflector; at least one light source disposed between the first reflector and the second reflector, an optical member spaced by a predetermined distance from the second reflector, wherein an air guide is defined between the second reflector and the optical member, wherein the second reflector comprises a specular reflection area and a diffuse reflection area, and wherein the specular reflection area occupies 5 to 50% of an entire area of the second reflector, characterized in that the second reflector comprises an inclined surface including a plurality of inclined surfaces having at least two inflection points, and concave lines and convex lines are alternately arranged along the inclined surface of the second reflector, the diffuse reflection area comprises first and second diffuse reflection areas (300b1, 300b2), configured so as to reflect incident light in a Lambertian distribution and/or a Gaussian distribution, an incidence angle of light incident upon each point of the first diffuse reflection area (300b1) is 55 degrees or more with respect to a normal line passing each point, an incidence angle of light incident upon each point of the second diffuse reflection area (300b2) is 60 degrees or more with respect to a normal line passing each point, a distance between the specular reflection area and the light source is less than that between the first diffuse reflection area and the light source, a distance between the first diffuse reflection area and the light source is less than that between the second diffuse reflection area (300b2) and the light source, and the first diffuse reflection area (300b1) is configured so that a quantity of light reflected in the Gaussian distribution is greater than a quantity of light reflected in the Lambertian distribution, and the second diffuse reflection area (300b2) is configured so that a quantity of light reflected in the Lambertian distribution is greater than a quantity of light reflected in the Gaussian distribution.