At the chromospheric level, a localized magnetic feature with polarity opposite to the underlying photospheric magnetic field has been observed in a rapidly formed sunspot. The strength of this reversed polarity is several hundred gauss. Seven subflares, centering around the reversed polarity, have been identified in observation of nine hours. The flares showed progressive increase in size and extent with the develop- ment of the reversed polarity. The bipolar feature above the unipolar magnetic flux can only mean that a bundle of magnetic lines of force has been kinked or knotted, or a self-closed flux system has been developed above the photosphere.