A processing apparatus for a base material tab protruding from a cylindrical electrode assembly includes: a vertical plate arranged in a second direction perpendicular to a first direction, the first direction being a longitudinal direction of the electrode assembly; a rotatable plate that is a planar plate arranged parallel to the vertical plate and coupled to be rotatable relative to the vertical plate; and a plurality of blades coupled between the vertical plate and the rotatable plate. The blades together form a variable diameter central area defined by ends of the blades according to the relative rotation of the rotatable plate to process the base material tab of the electrode assembly.