1. A learning machine comprising: a plurality of input-output signal registers connected in cascade, a plurality of weight memories for simultaneously outputting a plurality of weights, each of said weights to be multiplied by an output of a respective one of said plurality of input-output registers, a plurality of product-sum computing units each of which receives at different machine cycles a) an output signal of a respective one of said plurality of input-output signal registers and b) the weight stored in a respective one of said plurality of weight memories, each of said plurality of product-sum computing units for generating a product-sum, a single sigmoid function computing unit receiving product-sums at different machine cycles from all of Said plurality of product-sum computing units, said sigmoid function computing unit outputting output signals having a saturation characteristic with respect to each product-sum which is outputted by every one of said plurality of product-sum computing units.