An oxygen concentration detector comprises an oxygen ion conductive solid electrolyte body (1) and electrodes (4, 5, 14) provided thereon to form an oxygen concentration cell for detecting oxygen partial pressure in a gas such as exhaust gas from an internal combustion engine. The oxygen concentration detector according to the invention further comprises an AC power source supplying to the electrodes (4,14) an AC current having a frequency at which a polarization of alternating current component is caused mainly due to a polarization of the solid electrolyte body to heat it, and a DC power source (11) supplying a direct current to the electrodes (4, 5) so as to control oxygen concentration on the side of at least one electrode of the oxygen concentration cell to detect its electromotive force.