Disclosed is a neuron circuit in which an overflow signal before fire is retained after the fire. The neuron circuit according to an embodiment of the inventive concept includes a synapse element, a synaptic integration unit and a pulse generation unit. The synapse element receives output signals of a pre-neuron circuit and a post-neuron circuit. The synaptic integration unit includes a capacitor charged by the current flowing into the synapse element depending on the output signals of the pre-neuron circuit and the post-neuron circuit. The pulse generation unit generates an output pulse from the charging voltage of the capacitor. The pulse generation unit includes a pulse generation circuit generating the output pulse depending on the charging voltage of the capacitor and an overflow signal retaining unit connected between the capacitor and the pulse generation circuit and retaining an overflow signal, which exceeds a threshold voltage among the charging voltage of the capacitor after the pulse generation unit fires.