Disclosed is an operating method of a neural network processing device that communicates with an external memory device and executes a plurality of layers including obtaining layer information of the plurality of layers by analyzing a connection structure of the plurality of layers, generating an input address and an output address for a target layer based on the layer information, receiving expected input data and expected output data for the target layer, storing the expected input data at an input address area of the external memory device corresponding the input address, storing output result data at an output address area of the external memory device corresponding the output address by executing the target layer, comparing the output result data with the expected output data, and determining whether an error for the target layer occurs.