For example, the conductive fiber dispersion solution 140 may be prepared by adding the conductive fiber 131 to an organic solvent, such as N-methylpyrrolidone (NMP), o-dichlorobenzene, dichloroethane, dimethylformamide (DMF) and chloroform. [132] Subsequently, the conductive fiber dispersion solution 140 stored in the solution container 150 is filtered by the vacuum filter 160.