A small-signal power acquisition unit defines a threshold for each of a plurality of input signals based on a long-term average of a minimum power of the corresponding input signal, each of the input signals being obtained by a microphone, sets a power value of each input signal that is smaller than the corresponding defined threshold to be a small-signal power of the input signal. A correction amount setting unit obtains each correction amount for correcting the input signals based on the small-signal power of the corresponding input signal. A correction unit corrects each of the input signals based on each of the correction amounts for correcting the input signals.