A train-information management device comprising a central device (1-1, 11-1) that is connected to the Ethernet® provided over a plurality of vehicles (TC1, M2-1, M1-1, M2-2, M1-2, TC2) constituting a first train formation (B, B1) and that manages vehicle information in accordance with the Ethernet® protocol, wherein the central device is connected, in a first vehicle of the first train formation (B, B1), to an electric coupler via a first in-vehicle transmission line and a second in-vehicle transmission line, wherein said first and second in-vehicle transmission lines (4b, 14a) have a different transmission specification from each other, wherein the central device comprises: a hub; an information replacing unit provided between the first in-vehicle transmission line and the hub; a central processing unit that is configured to control the function of the central device, and to collect status data so as to collectively manage on-vehicle devices; and an information transmitting unit provided between the second in-vehicle transmission line and the hub, wherein the information replacing unit, the central processing unit, and the information transmitting unit are connected to the hub, wherein the information replacing unit is configured: to detect that a second formation including a train-information management device that manages vehicle information in accordance with an ARCNET protocol is coupled to the first vehicle in the first formation (B, B1) having the train-information management device, said detection being performed on the basis of contact information acquired from the electric coupler of the first vehicle in the first formation (B, B1); when coupling of the second formation is detected, to replace vehicle information from the first formation (B, B1) with vehicle information in accordance with the ARCNET protocol and output the replaced vehicle information to the second formation, and to replace the vehicle information from the second formation with the vehicle information in accordance with the Ethernet® protocol and output the replaced vehicle information to the first formation (B, B1), and wherein the information transmitting unit is configured: to detect that a third formation that manages vehicle information in accordance with the same protocol as the first formation (B, B1) is coupled to the first formation (B, B1), said detection being performed on the basis of contact information acquired from the electric coupler of the first vehicle in the first formation (B, B1); when coupling of the third formation is detected, to output vehicle information from the third formation to the first formation (B, B1), and to output the vehicle information from the first formation (B, B1) to the third formation. a hub; an information replacing unit provided between the first in-vehicle transmission line and the hub; a central processing unit that is configured to control the function of the central device, and to collect status data so as to collectively manage on-vehicle devices; and an information transmitting unit provided between the second in-vehicle transmission line and the hub, to detect that a second formation including a train-information management device that manages vehicle information in accordance with an ARCNET protocol is coupled to the first vehicle in the first formation (B, B1) having the train-information management device, said detection being performed on the basis of contact information acquired from the electric coupler of the first vehicle in the first formation (B, B1); when coupling of the second formation is detected, to replace vehicle information from the first formation (B, B1) with vehicle information in accordance with the ARCNET protocol and output the replaced vehicle information to the second formation, and to replace the vehicle information from the second formation with the vehicle information in accordance with the Ethernet® protocol and output the replaced vehicle information to the first formation (B, B1), and to detect that a third formation that manages vehicle information in accordance with the same protocol as the first formation (B, B1) is coupled to the first formation (B, B1), said detection being performed on the basis of contact information acquired from the electric coupler of the first vehicle in the first formation (B, B1); when coupling of the third formation is detected, to output vehicle information from the third formation to the first formation (B, B1), and to output the vehicle information from the first formation (B, B1) to the third formation.