1. A speech processing system comprising: a microphone array including a plurality of microphones, each of which inputs a sound mixture including speech of a speaker of interest and noise from a noise source region including a plurality of noise sources placed in a lateral direction with respect to the speaker of interest, and outputs a mixture signal including a speech signal and a noise signal, said plurality of microphones being arranged such that a difference between respective distances from said plurality of microphones to the speaker of interest becomes different from a difference between respective distances from said plurality of microphones to the noise source region; and a noise suppressor that suppresses the noise based on the mixture signals output from said plurality of microphones.