To provide a network connection device in which occurrence of a transmission line fault is easily recognized from a network equipment.

In a network connection device 10 which is connected to relay links 03, 04 face to face between two network devices 07, 08 and performs medium exchange between the network devices 07, 08 and between the relay links 03, 04, the network connection device is provided with a function for detecting reception interruption from the connected network equipment 07 or reception interruption from an opposed network connection device 11 as a transmission line fault, and a function for stopping transmission to the connected network equipment 07 immediately when the transmission line fault is detected.