A speech is recognized using ACF factors extracted from running autocorrelation functions calculated from the speech. The extracted ACF factors are a Wφ(0) (width of ACF amplitude around zero-delay origin), a Wφ(0)max (maximum value of the Wφ(0)), a τ1 (pitch period), a φ1 (pitch strength), and a Δφ1/Δt (rate of the pitch strength change). Syllables in the speech are identified by comparing the ACF factors with templates stored in a database.