A metal air battery includes a first battery cell module which generates electricity by oxidation of a metal and reduction of oxygen, a second battery cell module in fluid-communication with the first battery cell module and which generates electricity by oxidation of a metal and reduction of oxygen, and an air purifier in fluid-communication with the second battery cell module, where the air purifier purifies external air to supply first purified air to the second battery cell module, and the second battery cell module supplies second purified air generated by the oxidation of the metal and the reduction of the oxygen to the first battery cell module