1. A voice synthesis device, comprising: a memory unit operable to store, in advance for each voice quality, voice element information regarding a plurality of voice elements having the plural voice qualities that are different from each other; a voice information generating unit operable to acquire text data, and to generate, from plural pieces of the voice element information stored in said memory unit, synthetic voice information for each of the voice qualities, the synthetic voice information indicating synthetic voice having the voice quality which corresponds to a character that is included in the text data; a designating unit operable to place fixed points at N th dimensional coordinates for display where N is a natural number, the fixed points indicating voice quality of each piece of the voice element information stored in said memory unit, and to place plural set points at the coordinates for display on the basis of operation by a user so as to derive and designate a ratio at which changes each of plural pieces of the synthetic voice information which contributes to morphing along a time sequence on the basis of the placement of a moving point and the fixed points, the moving point continuously moving between the plural set points along the time sequence; a morphing unit operable to generate intermediate synthetic voice information using each of the plural pieces of synthetic voice information generated by said voice information generating unit with the ratio of change along the time sequence designated by said designating unit, the intermediate synthetic voice information indicating synthetic voice having intermediate voice quality, between the plural voice qualities, which corresponds to a character that is included in the text data; and a voice outputting unit operable to convert, to synthetic voice having the intermediate voice quality, the intermediate synthetic voice information generated by said morphing unit, and to output the resulting synthetic voice, wherein said voice information generating unit is operable to generate each of the plural pieces of synthetic voice information as a sequence of each of plural characteristic parameters, and said morphing unit is operable to generate the intermediate synthetic voice information by calculating an intermediate value of the plural characteristic parameters to which the plural pieces of synthetic voice information respectively correspond.