To improve peelability, yield in a peeling step, and yield in manufacturing a flexible device. A peeling method is employed which includes a first step of forming a peeling layer containing tungsten over a support substrate; a second step of forming, over the peeling layer, a layer to be peeled formed of a stack including a first layer containing silicon oxynitride and a second layer containing silicon nitride in this order and forming an oxide layer containing tungsten oxide between the peeling layer and the layer to be peeled; a third step of forming a compound containing tungsten and nitrogen in the oxide layer by heat treatment; and a fourth step of peeling the peeling layer from the layer to be peeled at the oxide layer.