1. A text-to-speech device comprising: a receiver to receive an input text which contains a peculiar expression; a normalizer to normalize the input text based on a normalization rule in which the peculiar expression, a normal expression for expressing the peculiar expression in a normal form, and an expression style of the peculiar expression are associated with one another, so as to generate one or more normalized texts; a selector to perform language processing with respect to each of the normalized texts, and select a single normalized text based on result of the language processing; a generator to generate a series of phonetic parameters representing phonetic expression of the single normalized text; a modifier to modify a phonetic parameter in the normalized text corresponding to the peculiar expression in the input text based on a phonetic parameter modification method according to the normalization rule of the peculiar expression; and an output unit to output a phonetic sound which is synthesized using the series of phonetic parameters including the modified phonetic parameter.