In an audio processing apparatus, a signal processor controls a volume of a sound signal provided to a sound emitting device. An adaptive filter determines an adaptive signal so as to minimize a magnitude of an error signal. A subtractor generates the error signal represented by a difference between the adaptive signal and an observation signal generated by a sound receiving device. A magnitude ratio calculator calculates a magnitude ratio of the observation signal relative to the error signal or a magnitude ratio of the adaptive signal relative to the error signal for each frame that is sequentially segmented from the error signal along a time axis. A controller variably controls a gain of the volume of the sound signal according to the magnitude of the error signal and the magnitude ratio.