An apparatus and method to successively extract a proper speech zone from speech inputted in such a fashion that noise is mixed in a speech to be recognized, and to remove noise from the detected speech zone. To this end, a noise position is estimated from an input waveform, a speech zone is detected from a speech inputted subsequently by using power information of speech at the estimated noise position, and noise is removed from the speech in the detected speech zone by using spectrum information of the speech at the estimated noise position. Further, the estimated noise zone is updated as appropriate by using a result of comparison between the power information of the input speech and the power information of the speech in the estimated noise zone so that the noise position is always properly estimated.