An onboard device (11; 12; 21; 22) configured to communicate with one or more other onboard devices (11; 12; 21; 22) in an onboard network, and configured to execute processing for updating of software of an own device while communicating with the other onboard devices (11; 12; 21; 22), the onboard device (11; 12; 21; 22) comprising an electronic control unit configured to: when not performing the processing for updating of software, execute software stored in a storage unit of the onboard device (11; 12; 21; 22) to generate first information, wherein the first information is data to be transmitted to the other onboard device (11; 12; 21; 22), the first information being information necessary for other onboard devices to execute functions thereof, wherein, in parallel, the other onboard device (11; 12; 21; 22) receives the first information, and operates based on the first information; when performing the processing of overwrite installing or other-face installing and activation for updating of software, generate second information to transmit to the other onboard device (11; 12; 21; 22) without executing the software, wherein the second information is information that temporarily substitutes for the first information and causes the functions of the other onboard device (11; 12; 21; 22) to be carried out in at least a limited and temporary way, wherein, in parallel, the other onboard device (11; 12; 21; 22) receives the second information, and operates in at least a temporary or partial way, based on the second information; and upon the processing of overwrite installing or other-face installing and activation for updating of software ending, execute the updated software stored in the storage unit to generate the first information, and control a communication unit of the onboard device (11; 12; 21; 22) to transmit the first information to the other onboard device (11; 12; 21; 22). when not performing the processing for updating of software, execute software stored in a storage unit of the onboard device (11; 12; 21; 22) to generate first information, wherein the first information is data to be transmitted to the other onboard device (11; 12; 21; 22), the first information being information necessary for other onboard devices to execute functions thereof, wherein, in parallel, the other onboard device (11; 12; 21; 22) receives the first information, and operates based on the first information; when performing the processing of overwrite installing or other-face installing and activation for updating of software, generate second information to transmit to the other onboard device (11; 12; 21; 22) without executing the software, wherein the second information is information that temporarily substitutes for the first information and causes the functions of the other onboard device (11; 12; 21; 22) to be carried out in at least a limited and temporary way, wherein, in parallel, the other onboard device (11; 12; 21; 22) receives the second information, and operates in at least a temporary or partial way, based on the second information; and upon the processing of overwrite installing or other-face installing and activation for updating of software ending, execute the updated software stored in the storage unit to generate the first information, and control a communication unit of the onboard device (11; 12; 21; 22) to transmit the first information to the other onboard device (11; 12; 21; 22).