A method of producing a carbon fiber composite material including: (a) masticating an elastomer to reduce the molecular weight of the elastomer to obtain a liquid elastomer; (b) mixing the elastomer obtained in the step (a) and carbon nanofibers having an average diameter of 0.5 to 500 nm to obtain a mixture; (c) increasing the molecular weight of the elastomer in the mixture obtained in the step (b) to obtain a rubbery elastic mixture; and (d) mixing the rubbery elastic mixture obtained in the step (c) to disperse the carbon nanofibers in the elastomer by a shear force to obtain a carbon fiber composite material.