Provided are a neural network device and a method of operation thereof. The neural network device for speaker recognition may include: a memory configured to store one or more instructions; and a processor configured to generate a trained second neural network by training a first neural network, for separating a mixed voice signal into individual voice signals by executing the one or more instructions, generate a second neural network by adding at least one layer to the trained first neural network, and generate a trained second neural network by training the second neural network, for separating the mixed voice signal into the individual voice signals and for recognizing a speaker of each of the individual voice signals.