Datagram transfer device with load distribution function

A datagram transmission apparatus comprising: a number of protocol termination units; and a destination processor, comprising: a routing section configured to determine a transmission destination route for a packet stream received from any one of the protocol termination units, the destination based on a combination of a stream identifier and a multipath identifier associated with the received one of The route selection section is configured to determine whether the transmission of the received packet stream to the transmission destination route is in a lock state and to select another transmission destination route if the transmission of the packet stream to the transmission destination route is in the lock state.