A light guide plate of an LED backlight unit is disclosed. The light guide plate comprises a pair of wide planes facing each other, and a narrow plane formed between the pair of wide planes and constituting a thickness of the light guide plate. The narrow plane has an incident plane formed on a section of the narrow plane facing the LED light source, and one of the wide planes constitutes an exiting plane from which light entered from the LED light source exits. The incident plane has a plurality of elliptic cylinder-shaped grooves carved into the incident plane in a thickness direction of the light guide plate. As such, the elliptic cylinder-shaped grooves are carved into the incident plane of the light guide plate in the thickness direction, widening an incidence angle of which light can be transmitted therethrough.