There is provided a method for manufacturing a carbon nanostructure with reduced occurrence of a bend and the like. The method for manufacturing a carbon nanostructure according to the present invention includes the steps of: preparing a base body formed of a catalyst member including a catalyst and a separation member that are in contact with or integral with each other (preparation step); oxidizing at least a part of a contact portion or integral portion of the catalyst member and the separation member (oxidation step); bringing a carbon-containing source gas into contact with the catalyst member and/or the separation member (CNT growth step); and growing a carbon nanostructure (CNT growth step). In the CNT growth step, the carbon nanostructure is grown in a separation interface region between the catalyst member and the separation member, by heating the base body while separating the separation member from the catalyst member.