A redox flow battery includes: first carbon nanotubes having an average diameter of 100 nm or r core, and second carbon nanotubes having an average diameter of 30 nm or less, in which the second carbon nanotubes are adhered to surfaces of the first carbon nanotubes such that the second carbon nanotubes bridge between the plural first carbon nanotubes. Since the redox flow battery includes an electrode material and an electrode including the electrode material, the electromotive force and the charging capacity are high.