A first embodiment of the present invention is a carbon fiber having a center line average roughness Ra for a single fiber surface of 6.0 – 13 nm with long diameter/short diameter of the single fiber being 1.11 – 1.245. The carbon fiber according to the first embodiment is obtained by fire resistance treatment and carbonization under specific conditions of a carbon fiber precursor acrylic fiber, which is a second embodiment, having a center line average roughness Ra for a single fiber surface of 18 – 27 nm with long diameter/short diameter of the single fiber being 1.11 – 1.245.