A neural network device according to an embodiment includes a plurality of neuron circuits, a plurality of synapse circuits, and a plurality of random number circuits. Each of the random number circuits outputs a random signal. Each of the synapse circuits receives the random signal from one of the random number circuits and updates a synaptic weight with a probability generated on the basis of the received random signal. The synapse circuits are divided into synapse groups. Each of two or more synapse circuits belonging to a first synapse group receives the random signal output from a first random number circuit. Each of two or more synapse circuits outputting output signals to a first neuron circuit belongs to a synapse group differing from a synapse group, to which other synapse circuits outputting the output signal to the first neuron circuit, belong.