A control apparatus that is connectable to a plurality of networks and transfers frames between the plurality of networks, the control apparatus comprising: a routing control unit configured to control transfer of the frames; and a plurality of controllers, each of which is provided for a corresponding one of the plurality of networks, each controller includes a transmission queue for receiving a frame from the corresponding network and inputting the frame to the routing control unit, for storing a frame that is output from the routing control unit and is to be transferred to the network serving as a transfer destination, and for transmitting the frame stored in the transmission queue to the network, wherein the routing control unit includes a buffer configured to store, among the inputted frames, a specified frame as a frame to be retransmitted, a normal transmission unit configured to output, among the inputted frames, a frame other than the frame to be retransmitted to the transmission queue of the controller corresponding to the network serving as the transfer destination, and, when the controller corresponding to the network serving as the transfer destination is in a full state in which no more frames cannot be stored in the transmission queue, to specify the inputted frame as the frame to be retransmitted and store the inputted frame in the buffer, and a signal handling unit configured to output, upon receipt of a cancellation signal indicating that the full state has been canceled from any of the plurality of controllers, to the transmission queue of the controller that has transmitted the cancellation signal, the frame to be retransmitted that is to be transferred to the network corresponding to the controller that has transmitted the cancellation signal; and the controller is configured to transmit, when the full state is canceled, the cancellation signal to the signal handling unit, the control apparatus further comprising a retry counter configured to show existence of the frame to be retransmitted for each of the plurality of networks, wherein the normal transmission unit is configured to refer to the retry counter, and to determine whether or not the controller corresponding to the network serving as the transfer destination is in the full state. a routing control unit configured to control transfer of the frames; and a plurality of controllers, each of which is provided for a corresponding one of the plurality of networks, each controller includes a transmission queue for receiving a frame from the corresponding network and inputting the frame to the routing control unit, for storing a frame that is output from the routing control unit and is to be transferred to the network serving as a transfer destination, and for transmitting the frame stored in the transmission queue to the network, wherein the routing control unit includes a buffer configured to store, among the inputted frames, a specified frame as a frame to be retransmitted, a normal transmission unit configured to output, among the inputted frames, a frame other than the frame to be retransmitted to the transmission queue of the controller corresponding to the network serving as the transfer destination, and, when the controller corresponding to the network serving as the transfer destination is in a full state in which no more frames cannot be stored in the transmission queue, to specify the inputted frame as the frame to be retransmitted and store the inputted frame in the buffer, and a signal handling unit configured to output, upon receipt of a cancellation signal indicating that the full state has been canceled from any of the plurality of controllers, to the transmission queue of the controller that has transmitted the cancellation signal, the frame to be retransmitted that is to be transferred to the network corresponding to the controller that has transmitted the cancellation signal; and the controller is configured to transmit, when the full state is canceled, the cancellation signal to the signal handling unit, the control apparatus further comprising a retry counter configured to show existence of the frame to be retransmitted for each of the plurality of networks, wherein the normal transmission unit is configured to refer to the retry counter, and to determine whether or not the controller corresponding to the network serving as the transfer destination is in the full state.