In an audio signal encoding apparatus, a first audio signal and a second audio signal are added into an addition-result signal. The first audio signal is subtracted from the second audio signal to generate a subtraction-result signal. A first difference signal is generated which represents a difference in the addition-result signal. A second difference signal is generated which represents a difference in the subtraction-result signal. A plurality of first predictors have different prediction characteristics respectively, and are responsive to the first difference signal for generating first different prediction signals for the first difference signal, respectively. A plurality of first subtracters operate for generating first prediction-error signals representing differences between the first difference signal and the first different prediction signals, respectively. A first minimum prediction-error signal representative of a smallest difference is selected from among the first prediction-error signals. A plurality of second predictors have different prediction characteristics respectively, and are responsive to the second difference signal for generating second different prediction signals for the second difference signal, respectively. A plurality of second subtracters operate for generating second prediction-error signals representing differences between the second difference signal and the second different prediction signals, respectively. A second minimum prediction-error signal representative of a smallest difference is selected from among the second prediction-error signals.