1. A speech processing device comprising: a sound source localization unit configured to determine a sound source position from acquired speech; a reverberation suppression unit configured to suppress a reverberation component of the speech to generate dereverberated speech; a feature quantity calculation unit configured to calculate a feature quantity of the dereverberated speech; a feature quantity adjustment unit configured to multiply the feature quantity by an adjustment factor corresponding to the sound source position to calculate an adjusted feature quantity; and a speech recognition unit configured to perform speech recognition using the adjusted feature quantity.