Included in a speech synthesizer, a natural language processing unit divides text data, input from a text input unit, into a plurality of components (particularly, words). An importance prediction unit estimates an importance level of each component according to the degree of how much each component contributes to understanding when a listener hears synthesized speech. Then, the speech synthesizer determines a processing load based on the device state when executing synthesis processing and the importance level. Included in the speech synthesizer, a synthesizing control unit and a wave generation unit reduce the processing time for a phoneme with a low importance level by curtailing its processing load (relatively degrading its sound quality), allocate a part of the processing time, made available by this reduction, to the processing time of a phoneme with a high importance level, and generates synthesized speech in which important words are easily audible.
SPEECH SYNTHESIZER, NAVIGATION APPARATUS AND SPEECH SYNTHESIZING METHOD