A manufacturing method of carbon nanofibers at a high activity is provided. Further, carbon nanofibers produced by the manufacturing method and being excellent in electric conductivity, crystallinity and dispersibility is provided.By a manufacturing method of carbon nanofibers in which an active species including cobalt as a chief component is employed as a catalyst and carbon monoxide is used as a carbon source, wherein said catalyst has 3 to 150 mass % of said active species carried on a carrier composed of a magnesium-containing oxide having a specific surface area of 0.01 to 5 m2/g, and a reaction temperature, partial pressure of carbon monoxide and a flow rate of raw material gas is controlled, CNFs that are excellent in electric conductivity, crystallinity and dispersibility can be manufactured at high activity, so that carbon nanofibers that is excellent in electric conductivity, crystallinity and dispersibility is obtained.