An extrusion molding apparatus for a light guide plate of a display device includes: a first surface of a first body and a second surface of a second body facing each other, the first body including a first side opposite to a second side thereof in a first direction, and a gap between the first and second surfaces, from which a light guide plate material is discharged along a second direction crossing the first direction. In the second direction, each of the first and second surfaces includes, in order: a first land portion; a manifold portion at a height different from the height of a first land portion; and a discharge portion from which the light guide plate material is discharged from the extrusion molding apparatus. Along the first direction, the gap at the discharge portion increases, and a width of the manifold portion in the second direction increases.