Abstract: A compact power storage system can efficiently generate electric power by storing surplus electric power, and can be constructed in a short working period without being restricted by conditions of the location where it is to be installed. The power storage system comprises a unitary electrolytic and fuel cell having a solid oxide electrolyte, a steam feed system for feeding steam to the cell, a hydrogen store and an oxygen store for storing hydrogen and oxygen produced in the cell, a heat-exchanger system for receiving heat of the exhaust from the cell, a space-heating hot water feed system for heating water using heat obtained from the exhaust, and a space-heating cold water feed system communicating with an absorption refrigerating machine for cooling water through the absorption process using heat obtained from the heat-exchanger system.