PURPOSE: To simplify a system by combining a feedforward network consisting of input units, hidden units, and output units with a Hopfield network consisting of units as many as the hidden units.

CONSTITUTION: The units 406 of the Hopfield network 404 receive the outputs of the hidden units 402 as inputs after they are passed through low-pass filters 411 to 415, and are coupled with all other units 406; and the coupling load increases in proportion to the product of the outputs of the units 406 at both the coupling ends at the time of learning and also decreases with a specific time constant. The outputs of the respective units 406 switch switches 405 provided between the corresponding hidden units 402 and output units 501. Thus, frequency components of an input signal are separated through the three-layered feedforward network and synchronizing frequency components are extracted by the Hopfield network 404.