An acquiring unit acquires pattern sentences, which are similar to one another and include fixed segments and non-fixed segments, and substitution words that are substituted for the non-fixed segments. A sentence generating unit generates target sentences by replacing the non-fixed segments with the substitution words for each of the pattern sentences. A first synthetic-sound generating unit generates a first synthetic sound, a synthetic sound of the fixed segment, and a second synthetic-sound generating unit generates a second synthetic sound, a synthetic sound of the substitution word, for each of the target sentences. A calculating unit calculates a discontinuity value of a boundary between the first synthetic sound and the second synthetic sound for each of the target sentences and a selecting unit selects the target sentence having the smallest discontinuity value. A connecting unit connects the first synthetic sound and the second synthetic sound of the target sentence selected.