A signal processing apparatus has a circuit network which is formed by connecting a plurality of neuron units into a network, each of the neuron being provided with a self-learning means having a weight function varying means and a weight function generating means for generating a variable weight function of the weight function varying means, on the basis of a positive or negative error signal obtained as a result of the comparison between an output signal and a teaching signal. In order to obtain a positive error signal .delta..sub.j(+) and a negative error signal .delta..sub.j(-), there is provided a differential coefficient calculating means for calculating two kinds of differential coefficients for a neuron response function, the calculation being done on the basis of the output signal from the neuron unit.