Abstract: [Problem ] The present invention addresses the problem of providing a novelnanocarbon composite which is used to achieve a stable and uniform mechanical strength improvement effect in a carbon fiber-reinforced plastic or carbon fiber-reinforced composite material impregnated with a nanocarbon-containing resin. [Solution] A novel nanocarbon composite containing nanocarbon and nano-cellulose modified with a functional group(s) or a novel nanocarbon composite containing nanocarbon, nano-cellulose modified with a functional group(s), and a affinitive binding agent is constituted by incorporating a resin serving as a matrix in a carbon fiber-reinforced plastic or carbon fiber-reinforced composite material.