An electrode system which includes: an electrode unit capable of switching at least a part of its shape between a curved shape and a stretched shape, wherein in the curved shape the electrode unit is wound around a predetermined linear tissue, and wherein in the stretched shape the electrode unit is flat and a treatment tool that switches the shape of the at least a part of the electrode unit between the curved shape and the stretched shape, wherein the electrode unit includes: an insulating member formed in a sheet shape out of an elastic material and an electrode that is disposed on a first surface which is an inside surface of a curvature when the insulating member has a curved shape and which applies a predetermined voltage.
