Disclosed is an optical network system including a upper network equipment, a lower network equipment, and a plurality of transfer network equipments connecting the upper network equipment and the lower network equipment through independent optical links, wherein the lower network equipment performs switching such that transmission and reception of an optical signal are performed through an optical link of a standby line when a failure occurs in at least one of an optical link used as a working line, an optical interface device associated with the working line in the upper network equipment, and a transfer network equipment associated with the working line.