A network hub connected to a bus of a first network and to a second network in an onboard network system that includes the first network, where transmission of first-type frames relating to traveling control of a vehicle is performed over said bus following a first communication protocol, and the second network, where transmission of second-type frames is performed following a second communication protocol that is different from the first communication protocol, the network hub comprising: a first reception buffer; a second reception buffer; a first transmission buffer; a second transmission buffer; a first reception unit configured to sequentially receive the first-type frames from the bus and to store data within the first-type frames in the first reception buffer; a second reception unit configured to sequentially receive the second-type frames from the second network and to store data within the second-type frames in the second reception buffer; a selecting unit configured to select which of the first network and second network the destination is for data that is the content of one of the first reception buffer and the second reception buffer, to store the data in the first transmission buffer in a case of having selected the first network, and to store the data in the second transmission buffer in a case of having selected the second network; a transmission unit configured to transmit yet-to-be-transmitted data in the first transmission buffer and yet-to-be-transmitted data in the second transmission buffer; and a degree-of-priority setting unit configured to set and store information indicating one of the first transmission buffer and second transmission buffer to give priority to; wherein the transmission unit is configured to perform priority transmission control, where yet-to-be-transmitted data in a priority transmission buffer that is one of the first transmission buffer and the second transmission buffer is transmitted with priority over yet-to-be-transmitted data in a non-priority transmission buffer that is the other, based on the priority information, wherein the priority information includes information for identifying the priority transmission buffer from the first transmission buffer and second transmission buffer, regarding which data should be transmitted with priority. a first reception buffer; a second reception buffer; a first transmission buffer; a second transmission buffer; a first reception unit configured to sequentially receive the first-type frames from the bus and to store data within the first-type frames in the first reception buffer; a second reception unit configured to sequentially receive the second-type frames from the second network and to store data within the second-type frames in the second reception buffer; a selecting unit configured to select which of the first network and second network the destination is for data that is the content of one of the first reception buffer and the second reception buffer, to store the data in the first transmission buffer in a case of having selected the first network, and to store the data in the second transmission buffer in a case of having selected the second network; a transmission unit configured to transmit yet-to-be-transmitted data in the first transmission buffer and yet-to-be-transmitted data in the second transmission buffer; and a degree-of-priority setting unit configured to set and store information indicating one of the first transmission buffer and second transmission buffer to give priority to; wherein the transmission unit is configured to perform priority transmission control, where yet-to-be-transmitted data in a priority transmission buffer that is one of the first transmission buffer and the second transmission buffer is transmitted with priority over yet-to-be-transmitted data in a non-priority transmission buffer that is the other, based on the priority information, wherein the priority information includes information for identifying the priority transmission buffer from the first transmission buffer and second transmission buffer, regarding which data should be transmitted with priority.