The invention relates to a laminate film, a backlight unit, and a liquid crystal display device, and a manufacturing method of the laminate film, wherein the laminate film can inhibit degradation of an optical functional layer due to invasion of oxygen and water vapor into the optical functional layer and also can reduces the thickness of the backlight unit. A laminate film includes a gas barrier film having a barrier layer and a support which supports the barrier layer stacked on one surface of an optical functional layer, in which the gas barrier film and the optical functional layer satisfy the following adhesion force conditions: an adhesion force between the support and the barrier layer is smaller than an adhesion force between the optical functional layer and the barrier layer, and an adhesion force between the support and the barrier layer is an adhesion force enabling peeling.