1. A speech processing apparatus, comprising: a segmenting unit configured to divide a fundamental frequency signal of a speech signal corresponding to an input text into a plurality of pitch segments, based on an alignment between samples of at least one given linguistic level included in the input text and the speech signal, wherein character strings of the input text are divided into the samples based on each linguistic level; a parameterizing unit configured to generate a parametric representation of the pitch segments by means of a predetermined invertible operator such as a linear transform, and generate a group of first parameters in correspondence with each linguistic level; a descriptor generating unit configured to generate, for each linguistic level, a descriptor that includes a set of features describing each sample in the input text; a model learning unit configured to classify the first parameters of each linguistic level of all speech signals in a memory into clusters based on the descriptor corresponding to the linguistic level, and learn, for each of the clusters, a pitch segment model for the linguistic level; and a storage unit configured to store the pitch segment models for each linguistic level together with mapping rules between the descriptors describing the features of the sample, for the linguistic level and the pitch segment models.