1. A speech synthesis system comprising a speech recognizer configured to recognize a speech signal; a sound signal acquirer configured to acquire a sound signal; a first spectrum acquirer configured to acquire a spectrum of the acquired sound signal as a first spectrum; a second spectrum generator configured to generate a reconfigured spectrum of the sound signal, based on the speech signal recognized by the speech recognizer, as a second spectrum; a modified spectrum generator configured to generate a modified spectrum in accordance with the first spectrum and the second spectrum; and an outputter configured to output a synthesized speech signal based on the modified spectrum.