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; a speech recognition unit configured to perform speech recognition using the adjusted feature quantity; and a model update unit configured to select a predetermined number of position-dependent acoustic models on the basis of the likelihood calculated by using the adjusted feature quantity and a position-dependent acoustic model of each sound source position and linearly combines model parameters of the selected position-dependent acoustic model to generate a position-dependent acoustic model corresponding to the sound source position, wherein the speech recognition unit performs speech recognition using the acoustic model generated by the model update unit.