A suction cup having an adsorption surface is provided wherein the suction cup has a disk-like main suction cup unit composed of an elastically-deformable material and has an attachment surface. The attachment surface has a gel layer composed of a gel, bonded thereto so as to cover the attachment surface. The adsorption surface is formed by the surface of the gel layer, and the gel layer are composed of a center portion composing the center of the adsorption surface, and a circumferential portion composing the outer circumference of the adsorption surface. The outer circumferential portion has the thickness larger than the thickness of the center portion.