A speech synthesizing system includes a unit (211, 212, 213, 24, 25, 27, 28) for generating a vowel signal, a unit (211, 214, 215, 26, 29, 22, 23) for generating a consonant signal, having a unit (214) for generating random data, a unit (12B) connected to the random data generation unit (214) to receive the random data therefrom, having first-order delaying function: 1/(sτ +α), for outputting first-order delayed random data, a unit (217) for selecting the vowel signal or the consonant signal in response to a selection signal; and a unit (216) for receiving an output signal from said selection unit (217) and filtering the received signal on the basis of a vocal tract simulation method. The first-order delayed random data from the first-order delaying unit (12B) are substantially applied to the vowel signal and/or the consonant signal.