A musical tone signal processing apparatus, the apparatus comprising: input means (11L, 11R) for inputting a musical tone signal, the musical tone signal comprising a signal for each of a plurality of input channels; dividing means (S12, S22) for dividing the signals into a plurality of frequency bands; level calculation means (S 13, S23) for calculating a level for each of the input channels for each of the frequency bands; localization information calculation means for calculating localization information, which indicates an output direction of the musical tone signal with respect to a first reference localization that has been set in advance, for each of the frequency bands based on the level; setting means (S100, S200) for setting at least one direction range of the output direction; judgment means (S101, S201) for judging whether the output direction of the musical tone signal is within the at least one direction range; retrieving means (S102, S202, S302) for retrieving at least one extraction signal comprising the signal of each of the input channels in the frequency bands from the dividing means (S12, S22) corresponding to the localization information calculated by the localization information calculation means having the output direction that is judged to be within the at least one direction range and an exclusion signal comprising the signals of each of the input channels in the frequency bands from the dividing means (S12, S22) corresponding to the localization information calculated by the localization information calculation means having the output direction that is judged to not be within any one of the at least one direction ranges; output signal generation means for generating an output signal in the time domain for each output channel that has been set in advance, the output signal in the time domain generated by signal processing and converting the at least one extraction signal and the exclusion signal; and output means (13L1, 13R1, 13L2, 13R2) for outputting the output signal in the time domain to each of the output channels. input means (11L, 11R) for inputting a musical tone signal, the musical tone signal comprising a signal for each of a plurality of input channels; dividing means (S12, S22) for dividing the signals into a plurality of frequency bands; level calculation means (S 13, S23) for calculating a level for each of the input channels for each of the frequency bands; localization information calculation means for calculating localization information, which indicates an output direction of the musical tone signal with respect to a first reference localization that has been set in advance, for each of the frequency bands based on the level; setting means (S100, S200) for setting at least one direction range of the output direction; judgment means (S101, S201) for judging whether the output direction of the musical tone signal is within the at least one direction range; retrieving means (S102, S202, S302) for retrieving at least one extraction signal comprising the signal of each of the input channels in the frequency bands from the dividing means (S12, S22) corresponding to the localization information calculated by the localization information calculation means having the output direction that is judged to be within the at least one direction range and an exclusion signal comprising the signals of each of the input channels in the frequency bands from the dividing means (S12, S22) corresponding to the localization information calculated by the localization information calculation means having the output direction that is judged to not be within any one of the at least one direction ranges; output signal generation means for generating an output signal in the time domain for each output channel that has been set in advance, the output signal in the time domain generated by signal processing and converting the at least one extraction signal and the exclusion signal; and output means (13L1, 13R1, 13L2, 13R2) for outputting the output signal in the time domain to each of the output channels.