A cushion includes a first member and a second member. The first member includes a first body and at least one first extending portion. At least one sidewall of the first extending portion has a first protruding portion. The second member includes a second body and a plurality of second extending portions. At least one sidewall of each second extending portion has at least one second protruding portion corresponding to the first protruding portion. When the first member and the second member are assembled, the first extending portion and the second extending portions are staggered with each other. When the first member and the second member move away from each other by a predetermined distance, the first protruding portion is clamped to the second protruding portion.