1. A speech synthesis information editing apparatus comprising: a phoneme storage unit configured to store phoneme information that designates a duration of each phoneme of speech to be synthesized; a feature storage unit configured to store feature information that designates a time variation in a feature of the speech; an expansion/compression rate storage unit configured to store a phoneme expansion/compression rate that is set for each phoneme; an edition processing unit configured to change a duration of each phoneme designated by the phoneme information in accordance with an expansion/compression degree that is provided for each phoneme, wherein the expansion/compression degree is obtained according to the feature designated by the feature information for the phoneme and the phoneme expansion/compression rate that corresponds to the phoneme; and a display control unit configured to display a phoneme indicator having a length set according to the duration of each phoneme designated by the phoneme information, and configured to update the displayed length of the phoneme indicator based on the duration of each phoneme changed by the edition processing unit.