PURPOSE: To make optical lateral inhibition relatively easily by distributing part of light outputted from a modulator to the detector of a nearby node as a lateral inhibition signal.

CONSTITUTION: Each node has a modulator 3 which is connected to a detector 5 by an electric circuit 4, and an optical element 6. An encoded input light signal A is inputted to the modulator 3. The light signal B outputted from the modulator 3 is inputted to the corresponding optical element 6. At this element, a refracted light signal C becomes the output signal of a layer 1. A reflected light signal D, on the other hand, is inputted to the nearby node as a regressive lateral inhibition signal. Each modulator 3 is a type having an output signal which decreases as the signal received from the corresponding detector 5 increases. Therefore, the output signal B of the modulator corresponding to a detector 5 decreases as the intensity of the inhibition signal detected by the detector 5 is larger. Consequently, the output signal C also decreases.