A method of manufacturing a carbon nanotube composite includes: a laminate forming step of forming, on a conductive base material made of a first metal having conductivity, a buffer layer made of a second metal capable of mutual diffusion with the first metal, and forming, on the buffer layer, a catalyst layer made of seed catalyst particles which catalyze formation of carbon nanotubes; a buffer layer diffusion step of performing heat treatment on the laminate; and a carbon nanotube layer forming step of forming the carbon nanotubes on the catalyst layer of the laminate by a chemical vapor deposition method, wherein the heat treatment is performed so as to form a solid phase diffusion region where the first metal and the second metal are solid-phase diffused from a surface of the conductive base material to a predetermined depth selected from depths of 850 nm or more.