The electronic display board system with a modified Ethernet network according to the present invention comprises a main controller 1 provided with a main Ethernet switch 10 comprising a first main port 101 and a second main port 102; and first to Nth display units D1, D2, . . . , DN (N is an integer of 2 or more) sequentially connected with each other by an Ethernet network to receive image data transmitted from the main controller 1 to output the data on a display module 21 or transmit the data to a neighboring display unit or the main controller 1, wherein the first to Nth display units D1, D2, . . . , DN each comprise a first sub-port 201 and a second sub-port 202 to receive a first image data transmitted from the second main port 102 to transmit the data in a forward direction and to receive a second image data transmitted from the first main port 101 to transmit the data in a reverse direction.