Using a device for producing nanocarbon, a fluidized bed is formed by supplying a low hydrocarbon and oxygen to a fluid catalyst, and nanocarbon and hydrogen are produced by a decomposition reaction of the low hydrocarbon accompanied by a self-combustion of the low hydrocarbon and the oxygen. The device includes: a fluidized bed reactor for containing the fluid catalyst and for causing the self-combustion thereof while being supplied with the low hydrocarbon and the oxygen; a gas supplying unit connected to the fluidized bed reactor for supplying the low hydrocarbon and the oxygen to the fluidized bed reactor; an exhaust gas path connected to the fluidized bed reactor for exhausting an exhaust gas in the fluidized bed reactor to outside; and a supplying unit connected to the fluidized bed reactor for supplying the fluid catalyst to the fluidized bed reactor.