Abstract: [Problems to be Solved] The invention provides inexpensive carbon fiber filler material, which has a low content of metal impurity and enables the resin composite material to exhibit conductivity when added thereto in a small amount. [Means to Solve the Problem] (1) carbon nanofiber containing iron (Fe) of 6 mass % or less and vanadium (V) of 3 mass % or less as a metal impurity other than carbon, which does not substantially contain metal elements other than Fe and V, (2) a method for producing carbon nanofiber characterized in contacting a catalyst in which Fe and V are supported on a carbon support and a carbon-containing compound at a high temperature, (3) a resin composite material in which the carbon nanofiber is blended and (4) use thereof.