A free-standing membrane electrolyte electrode assembly (ESC) comprises an electrolyte, an anode electrode formed at one end face of the electrolyte, and a cathode electrode formed at the other. The electrolyte is a single crystal having a surface along with oxide ions move or a direction in which the ions move or a polycrystal oriented along a surface along which oxide ions move or in a direction in which the ions move. The surface or the direction is parallel to the thickness direction. The thickness of the electrolyte is 50 to 800 μm and the quotient of the division of the total thickness of the anode electrode and the cathode electrode by the thickness of the electrolyte is 0.1 or less,. The thickness of the ESC is 1 mm or less.