The invention relates to (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. According to the invention, an inexpensive carbon fiber filler material can be obtained which has a low content of metal impurities and enables to exhibit electric conductivity when added to resin in a small amount.