Provided is a method for highly actively producing carbon nanofibers. Also provided are carbon nanofibers that are obtained by said production method and that have excellent conductivity, crystallinity, and dispersibility. A carbon nanofiber production method that uses carbon monoxide as a carbon source and that uses as a catalyst an active species that has cobalt as a main component. The catalyst includes a carrier that has a specific surface area of 0.01-5 m2/g, that comprises an oxide that contains magnesium, and that supports 3-150 mass% of the active species. Carbon nanofibers that have excellent conductivity, crystallinity, and dispersibility can be more actively produced by controlling reaction temperature, the partial pressure of the carbon monoxide, and the flow rate of a raw material gas, and carbon nanofibers that have excellent conductivity, crystallinity, and dispersibility can be obtained.