6. The voice synthesis device according to claim 1 , further comprising: an image storing unit operable to store, in advance for each of the voice quality, image information indicating an image which corresponds to each of the voice quality; an image morphing unit operable to generate, from a plural pieces of the image information, intermediate image information indicating an image which corresponds to each of the voice quality of the intermediate synthetic sound information; and a display unit operable to acquire the intermediate image information generated by said image morphing unit, and to display the image indicated by the intermediate image information in synchronization with the synthetic voice outputted from said voice outputting unit.
6. The voice synthesis device according to claim 1 , further comprising: an image storing unit operable to store, in advance for each of the voice quality, image information indicating an image which corresponds to each of the voice quality; an image morphing unit operable to generate, from a plural pieces of the image information, intermediate image information indicating an image which corresponds to each of the voice quality of the intermediate synthetic sound information; and a display unit operable to acquire the intermediate image information generated by said image morphing unit, and to display the image indicated by the intermediate image information in synchronization with the synthetic voice outputted from said voice outputting unit. 7. The voice synthesis device according to claim 6 , wherein the plural pieces of image information respectively indicate face images which correspond to each of the voice quality.