The present invention relates to a buffer circuit of a semiconductor memory device, and includes a common bias supply unit and a plurality of interface units having a differential amplifying structure. Each interface unit receives an input signal and differentially amplifies the input signal and a common bias. The common bias supply unit is driven by a reference voltage to provide the common bias signal to each of the interface units. The buffer circuit makes it possible to reduce the area occupied by the buffer circuit in a semiconductor memory device.