Disclosed herein is a signal processing apparatus, including: removal means for removing, from a sound signal in the form of a stereo signal, a center component which is a component of sound positioned at the center between the left and the right; extraction means for extracting, from the sound signal from which the center component is removed, first feature quantity representative of characteristics of sounds of different tones of the 12-tone equal temperament within a predetermined range; and decision means for deciding a chord within the predetermined range using the first feature quantity.