1. A segment information generation device comprising: a waveform cutout unit implemented at least by hardware including a processor that cuts out a speech waveform from natural speech at a time period not depending on a pitch frequency of the natural speech, continuously; a feature parameter extraction unit implemented at least by hardware including a processor that extracts a feature parameter of a speech waveform from the speech waveform cut out by the waveform cutout unit; a time domain waveform generation unit implemented at least by hardware including a processor that generates a time domain waveform based on the feature parameter; a spectrum shape change degree estimation unit implemented at least by hardware including a processor that estimates a degree of change in spectrum shape indicating a degree of change in spectrum shape of natural speech; and a period control unit implemented at least by hardware including a processor that determines a time period to cut out a speech waveform from the natural speech based on the degree of change in spectrum shape.
7. The segment information generation device according to claim 1 , further comprising: a spectrum shape change degree estimation unit comprising a processor that estimates a degree of change in spectrum shape indicating a degree of change in spectrum shape of natural speech.