PURPOSE: To extract an accurate fundamental frequency by accurately detecting an epoch point corresponding to the fundamental frequency.

CONSTITUTION: A perception type neural network after a learning process by an error reverse propagating method is used, and a forward propagation process 16 and a zero-crossing detection process 17 are performed to accurately detect the time of the epoch point corresponding to the fundamental frequency by a nonlinear emphasizing process characteristic to the neural network. In a fundamental frequency calculating process 18, the fundamental frequency is calculated from the interval of the time of the epoch point to accurately extract the fundamental frequency.