A gateway connected to a bus used for communication by a plurality of ECUs provided on-board a vehicle is provided with: an external communication unit that receives, from a server external to the vehicle, firmware update information that includes updated firmware for one ECU from among the plurality of ECUs; an ECU information acquiring unit that acquires system configuration information indicating the type of each of the plurality of ECUs connected to the bus; and a FW update processing unit that performs a controlling operation to update firmware of the relevant ECU based on the updated firmware, after an operation verification of the updated firmware is performed using an ECU of each type indicated by the system configuration information.