The flow battery according to the present disclosure comprises a first non-aqueous liquid, a first electrode in contact with the first non-aqueous liquid, a second electrode which serves as a counter electrode of the first electrode, and a lithium ion conductive film which separates the first electrode and the second electrode from each other. The lithium ion conductive film is formed of a polymer base material containing an ionic polymer. The polymer base material has an interspace which communicates with an outside thereof. The polymer base material is formed of at least one kind of resin selected from the group consisting of a thermosetting resin and a thermoplastic resin which has a melting point of not less than 150 degrees Celsius. The ionic polymer is contained in an inside of the interspace of the polymer base material. The ionic polymer is represented by where n1 and n2 are, each independently, natural numbers of not less than 1, or where m1, m2, n1, and n2 are, each independently, natural numbers of not less than 1. The flexible lithium ion conductive film having a low swelling property when in contact with a non-aqueous liquid.