A product-sum operation device includes a product operator, a sum operator, and a malfunction determiner. The product operator includes a plurality of product operation elements (10AA) to (10AC), and each of the plurality of product operation elements (10AA) to (10AC) is a resistance change element. The sum operator includes an output detector that detects the sum of outputs from the plurality of product operation elements (10AA) to (10AC). The malfunction determiner determines that a malfunction has occurred when the sum detected by the output detector exceeds a specified value. The specified value is a value equal to or greater than a maximum value of the sum that can be detected by the output detector when the plurality of product operation elements (10AA) to (10AC) all operate normally.