1. A neural network circuit including a plurality of neuron circuits, comprising: a plurality n of input terminals for receiving input signals, where n is an integer greater than 1; two weight coefficients corresponding to each of said input terminals; a subtraction circuit for calculating a difference between one of the weight coefficients and an input signal; a calculation circuit for executing a squaring operation on a subtraction result of said subtraction circuit; a multiplication circuit for multiplying an output signal of said calculation circuit by another of said weight coefficients; an addition circuit for accumulating all results of calculations performed on said plurality n of input signals and 2n weight coefficients obtained from said multiplication circuit; a threshold circuit having a predetermined threshold value for determining a magnitude of a result of said accumulation in accordance with said predetermined threshold value, and outputting said accumulation result wherein, said neuron circuits are unit circuits and use the output results of said threshold value circuit as output signals; and means for connecting input and output terminals of said neuron circuits, said neuron circuits having independent said weight coefficients with respect to a plurality of said input signals inputted into said network circuit executing calculations, an output value of at least one of said neuron circuits being an output signal of said network circuit, and said two weight coefficients and a size of said threshold value of said threshold value circuit controlling said network circuit.