The purpose of the present invention is to provide a metal-oxygen battery in which moisture, carbon dioxide or the like contained in air does not enter therein and oxygen can be supplied thereto stably regardless of the type of a light beam to be employed to achieve charge/discharge. [Solution] A metal-oxygen battery (1) comprises a positive electrode (2) which contains oxygen as an active material, a negative electrode (3) which contains a metal as an active material, an electrolyte layer (4) which is arranged between the positive electrode (2) and the negative electrode (3), and a case (5) which accommodates the positive electrode (2), the negative electrode (3) and the electrolyte layer (4) in a tightly sealed manner. The positive electrode (2) contains an oxygen-storing material which has a catalytic function for a battery reaction and also has a function of ionizing oxygen and binding ionized oxygen to a metal ion that transfers from the negative electrode (3) to the positive electrode (2) through the electrolyte layer (4) to thereby produce a metal oxide when the battery is discharged, or of reducing the metal oxide and storing oxygen when the battery is charged.