1. A speech synthesis apparatus comprising: a text analysis unit configured to analyze an input text and output language information including information on prosodic control of speaker; a dictionary storage unit configured to store a first prosodic control dictionary of a target speaker and a second prosodic control dictionary of each of a plurality of standard speakers; a prosodic parameter generation unit configured to generate a first prosodic parameter using the first prosodic control dictionary and generate a plurality of second prosodic parameters using the second prosodic control dictionary, based on the language information, the first prosodic parameter changing between speakers and being generated for each speaker; a normalization unit configured to normalize the plurality of second prosodic parameters based a normalization parameter, the normalized second prosodic parameters each being close to the first prosodic parameter, the normalization parameter being set to a sum of a difference and a threshold, the sum being added to an F 0 pattern of each of the plurality of standard speakers, the difference being calculated by subtracting an average of an F 0 pattern of each of the plurality of standard speakers from an average of an F 0 pattern of the target speaker; a prosodic parameter interpolation unit configured to interpolate the first prosodic parameter and the plurality of normalized second prosodic parameters based on weight information to generate a third prosodic parameter; a speech synthesis unit configured to generate synthesized speech in accordance with the third prosodic parameter; and a normalization parameter generation unit configured to generate the normalization parameter based on a first predetermined prosodic parameter statistic corresponding to the first prosodic control dictionary and a second predetermined prosodic parameter statistic corresponding to the second prosodic control dictionary.