A backlight unit includes a rectangular light guide plate including a first edge and a second edge orthogonally crossing each other. A light source arranged on a flexible substrate emits light to the first edge of the light guide plate and then the light emitted from the light source is emitted to outside from an upper surface of the light guide plate. A connection flexible substrate is connected to the flexible substrate and arranged along the second edge of the light guide plate to outside of the backlight unit. The second edge of the light guide plate facing the connection flexible substrate is cut out at an acute angle to the first edge of the light guide plate to pass around the connection flexible substrate.