NOVELTY - A negative electrode active material (10) comprises composite particles (11) containing tin and cobalt, and carbon nanofibers (12). A portion or all of carbon nanofibers is located in the inside of composite particles. The composite particles have a structure containing cobalt centering on the tin, or cobalt unevenly distributed in the outer surface of tin. The composite particles have average particle diameter of 0.1-10 mu m. The content of carbon nanofibers with respect to total amount of tin and cobalt is 1-20 %mass.    USE - Negative electrode active material is used for lithium-ion secondary battery (claimed) used for portable electronic device e.g. mobile telephone and notebook computer, and electric vehicle.    ADVANTAGE - The negative electrode active material has excellent hardness and electroconductivity, and provides lithium-ion secondary battery with excellent cycle characteristics, output characteristics, and crack generation-proof property by volume expansion of composite particles, and high capacity, and is manufactured by economical process.    DETAILED DESCRIPTION - A negative electrode active material comprises composite particles containing tin and cobalt, and carbon nanofibers. A portion or all of carbon nanofibers is located in the inside of composite particles, and the remainder portion or all of carbon nanofibers is located in the exterior of composite particles. The composite particles have a structure containing cobalt centering on tin, or cobalt unevenly distributed in the outer surface of tin. The composite particles have average particle diameter of 0.1-10 mu m. The content of carbon nanofibers with respect to total amount of tin and cobalt is 1-20 %mass. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of negative electrode active material; and    (2) lithium-ion secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of negative electrode active material. (Drawing includes non-English language text)    Negative electrode active material (10)    Composite particles (11)    Particle portion (11a)    Coating portion (11b)    Carbon nanofibers (12)