A sum-of-products operator including: a first circuit configured to generate a plurality of signals, each of which corresponds to each of a plurality of data; a second circuit including a first operation circuit configured to multiply each of the signals generated by the first circuit by a weight using a plurality of variable resistive elements having variable resistance values, and to calculate a sum of a plurality of results of multiplications; a third circuit configured to calculate a result of summing values corresponding to the data or a result of the summing value after being adjusted; and a fourth circuit including a differential circuit configured to output a difference between a calculated result in the first operation circuit of the second circuit and a calculated result in the third circuit.