The edge states in the quantum Hall regime are forced to interfere on one side of an Aharonov-Bohm ring by a potential barrier. The net effect of the interference caused by the potential barrier is found to change the electron's phase by Delta in the final transmittance, and the phase shift Delta is continuous as the barrier potential is continuously changed. This result is in sharp contrast with the earlier study that Delta = 2npi, where n is an integer, regardless of the barrier potential. (C) 2002 Elsevier Science Ltd. All rights reserved.