Envelope identification section generates input envelope data (DEVin) indicative of a spectral envelope (EVin) of an input voice. Template acquisition section reads out, from a storage section, converting spectrum data (DSPt) indicative of a frequency spectrum (SPt) of a converting voice. On the basis of the input envelope data (DEVin) and the converting spectrum data (DSPt), a data generation section specifies a frequency spectrum (SPnew) corresponding in shape to the frequency spectrum (SPt) of the converting voice and having a substantially same spectral envelope as the spectral envelope (EVin) of the input voice, and the data generation section generates new spectrum data (DSPnew) indicative of the frequency spectrum (SPnew). Reverse FFT section and output processing section generates an output voice signal (Snew) on the basis of the new spectrum data (DSPnew).