A metal-air battery includes a unit cell wound into a roll. The unit cell includes a negative-electrode metal layer having a first surface located in a circumferential direction of the roll and a second surface facing the first surface and located in the circumferential direction of the roll; a first electrolyte film and a first positive-electrode layer sequentially disposed on the first surface of the negative-electrode metal layer; and a second electrolyte film and a second positive-electrode layer sequentially disposed on the second surface of the negative-electrode metal layer. The unit cell is wound in a way such that the first positive-electrode layer and the second positive-electrode layer face each other.