A transmission apparatus used for resolving an ATM address and provided between a terminating node communicating with another terminating node by using a layer-3 address and an ATM-switch network. A transmission apparatus includes a first apparatus which receives an ATM address of another transmission apparatus and a layer-3 address of a terminating node connected to another transmission apparatus from another transmission apparatus, and catalogs ATM address and layer-3 address into a table, and a second apparatus which searches the table using a layer-3 address of a destination terminating node which is a destination of a transmission of data received from a source terminating node connected to a transmission apparatus to acquire an ATM address of another transmission apparatus connected to destination terminating node, and communicates with another transmission apparatus by using the acquired ATM address to transmit a cell including information of a layer-3 address of destination terminating node.