In an audio signal processing apparatus, a generation section generates an audio signal representing a voice. A distribution section distributes the audio signal generated by the generation section to a first channel and a second channel, respectively. A delay section delays the audio signal of the first channel relative to the audio signal of the second channel for creating a phase difference between the audio signal of the first channel and the audio signal of the second channel such that the created phase difference has a duration corresponding to either an added value of a first duration which is approximately one half of a period of the audio signal generated by the generation section and a second duration which is set shorter than the first duration, or a difference value of the first duration and the second duration. An addition section adds the audio signal of the first channel and the audio signal of the second channel with one another, between which the phase difference is created by the delay section, and outputs the added audio signal which represents natural voice with various characteristics.