A method of processing a 2-channel stereo sound signal into a spatial stereo sound includes generating stereo signals of first and second channels from a first input channel signal and a second input channel signal by applying a time difference of times taken for each channel signal to arrive at two ears, and a sound pressure difference formed between the two ears and varying with respect to a frequency band or constant, to each of the first and second input channel signals, generating a center channel of the first and second channel by adding the first and second input channel signals, generating a surround signal of the first channel by subtracting one of the first and second input channel signals, from the other one of the first and second input channel signals, and generating a surround signal of the second channel by making the surround signal of the first channel out of phase, generating a plurality of reflected sounds from the generated surround signals, and applying the time difference and the sound pressure difference to each reflected sound, processing reflected signals of the first and second channels from the reflected sounds, and adding the generated signals of the first channel and adding the generated signals of the second channel.