A method for processing carbon nanotubes includes positioning in a treatment chamber of a carbon nanotube processing apparatus a substrate having multiple carbon nanotubes bundled together and oriented substantially perpendicular to a surface of the substrate, and introducing a microwave into the treatment chamber from a planar antenna having multiple microwave radiation holes such that plasma of an etching gas is generated and that the plasma etches the carbon nanotubes starting from one end of the carbon nanotubes bundled together.