A redox flow battery includes first and second electrodes, a separator separating the first and second electrodes, an active material, an electrolytic solution containing a redox species, and a circulation mechanism. The active material is insoluble in the electrolytic solution. The circulation mechanism circulates the electrolytic solution between the first electrode and the active material. The redox species performs oxidation and reduction at the first electrode and is oxidized and reduced by the active material. The circulation mechanism includes an electrolytic solution container containing the active material and a permeation preventing unit. The electrolytic solution is brought into contact with the active material in the electrolytic solution container, and the redox species is oxidized and reduced by the active material. The permeation preventing unit is disposed adjacent the outlet for the electrolytic solution of the electrolytic solution container and prevents permeation of the active material.