A method for manufacturing a carbon nanostructure according to an embodiment of the present invention is a method for manufacturing a carbon nanostructure, the method including a preparation step of preparing a substrate containing a carburizable metal as a main component, and a carbon nanostructure growth step of supplying a carbon-containing gas while heating the substrate, in which the carbon nanostructure growth step includes gradually cleaving a heated portion of the substrate. The cleaving in the carbon nanostructure growth step is preferably performed by subjecting the substrate to shearing. The heating in the carbon nanostructure growth step is preferably performed by irradiating a cleaving portion of the substrate with a laser. The preparation step preferably includes forming, in the substrate, a notch for inducing cleavage. Preferably, the substrate in the carbon nanostructure growth step is not oxidized.