1. A signal processing device performing a subband analysis process on an input signal, characterized by comprising: analysis filter process means for performing an analysis filter process on every N samples of real-valued input data and outputting K samples of real-valued data if K=4N, where K is the number of subbands and N is a decimation ratio; and GDFT/SSB modulation batch process means for performing a GDFT process, which is a Generalized Discrete Fourier Transformation process, and an SSB modulation process, which is a single sideband modulation process, by a product arithmetic in batch between a (K/2)×K real-valued matrix and a K×1 real-valued matrix, on the K samples of real-valued data inputted from the analysis filter process means, and outputting 1 sample×(K/2) channel of real-valued subbands data.