A frame transmission prevention apparatus in a network system (10; 11) including a plurality of electronic control units (100a-100d) communicating with one another via a network, the apparatus being connected to the network, the apparatus comprising: a reception unit (410; 2410) adapted to receive a frame from the network; a processing unit (440; 2420) adapted to switch whether to perform a predetermined process for preventing transmission of the frame received by the reception unit (410; 2410) if the received frame satisfies a predetermined condition, on the basis of management information indicating whether prevention of transmission of a frame is permitted; and a storage unit (441;2430) adapted to store the management information; characterized by an update unit (460; 2450) adapted to update the management information stored in the storage unit (441; 2430), wherein the management information includes, for each of a plurality of identifiers, flag information indicating whether prevention of transmission of a frame that has the identifier and that satisfies the predetermined condition is permitted, wherein if the frame received by the reception unit (410; 2410) satisfies the predetermined condition and if the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is permitted, the processing unit performs the predetermined process, wherein if the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is not permitted, the processing unit does not perform the predetermined process, wherein in the case where the frame received by the reception unit (410; 2410) satisfies the predetermined condition and the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is not permitted, if the update unit (460; 2450) detects that a predetermined particular electronic control unit among the plurality of electronic control units (100a-100d) is anomalous, the update unit (460; 2450) updates the flag information so that the prevention is permitted, and wherein the network includes a plurality of buses, the frame transmission prevention apparatus is a gateway apparatus having a function of connecting the plurality of buses to one another and of forwarding a frame received from one bus to another bus, the predetermined process for preventing transmission of the frame that satisfies the predetermined condition includes a process of preventing the forwarding of the frame received by the reception unit (410; 2410). a reception unit (410; 2410) adapted to receive a frame from the network; a processing unit (440; 2420) adapted to switch whether to perform a predetermined process for preventing transmission of the frame received by the reception unit (410; 2410) if the received frame satisfies a predetermined condition, on the basis of management information indicating whether prevention of transmission of a frame is permitted; and a storage unit (441;2430) adapted to store the management information; characterized by an update unit (460; 2450) adapted to update the management information stored in the storage unit (441; 2430), wherein the management information includes, for each of a plurality of identifiers, flag information indicating whether prevention of transmission of a frame that has the identifier and that satisfies the predetermined condition is permitted, wherein if the frame received by the reception unit (410; 2410) satisfies the predetermined condition and if the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is permitted, the processing unit performs the predetermined process, wherein if the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is not permitted, the processing unit does not perform the predetermined process, wherein in the case where the frame received by the reception unit (410; 2410) satisfies the predetermined condition and the flag information corresponding to the identifier of the frame indicates that prevention of transmission of the frame is not permitted, if the update unit (460; 2450) detects that a predetermined particular electronic control unit among the plurality of electronic control units (100a-100d) is anomalous, the update unit (460; 2450) updates the flag information so that the prevention is permitted, and wherein the network includes a plurality of buses, the frame transmission prevention apparatus is a gateway apparatus having a function of connecting the plurality of buses to one another and of forwarding a frame received from one bus to another bus, the predetermined process for preventing transmission of the frame that satisfies the predetermined condition includes a process of preventing the forwarding of the frame received by the reception unit (410; 2410).