1. A speech processing system comprising: at least one hardware processor configured to implement: a linear microphone array comprising a plurality of microphones, arranged on a straight line, each of which inputs speech of a speaker of interest and noise from a noise source region comprising a plurality of noise sources, and outputs a mixture signal comprising said speech and said noise; and a noise suppressor that suppresses said noise based on said mixture signals, wherein a direction of arranging the plurality of microphones in said linear microphone array is determined such that said straight line is perpendicular to a longitudinal axis of said noise source region, and a distance, between said linear microphone array and said noise source region, and a tilt of a placement plane of said microphone array are adjusted so as to decrease differences between respective distances from each of noise sources in said noise source region to the plurality of microphones in said linear microphone array.