A flow battery includes: a cell including a first chamber and a second chamber a first liquid that contains a charge mediator and a discharge mediator, and that is located in the first chamber of the cell; a first electrode located in the first chamber of the cell; a first active material that is solid and that is located in the first chamber of the cell; a second liquid located in the second chamber of the cell; a second electrode that is located in the second chamber of the cell, and that is a counter electrode to the first electrode; and a first stirrer that stirs the first liquid in the first chamber. The charge mediator has a lower equilibrium potential than an equilibrium potential of the first active material. The discharge mediator has a higher equilibrium potential than the equilibrium potential of the first active material.