A backlight unit according to various embodiments of the disclosure may include a light source, a light guide plate configured to guide light emitted from the light source and disposed to face in a first direction, and an optical film disposed over the light guide plate. The optical film may include a first prism sheet including first prism structures arranged side by side to each other along a second direction perpendicular to the first direction, and a second prism sheet disposed over the first prism sheet and including second prism structures arranged side by side to each other along a third direction forming an acute angle with the second direction.