An in-vehicle network system which is adapted to be mountable on a vehicle, comprising: a plurality of electronic control units (50-1, 50-2), wherein a first group of devices including a first electronic control unit and one or more first sensor devices, and a second group of devices including a second electronic control unit and one or more second sensor devices are provided, wherein a plurality of sensor devices including the one or more first sensor devices and one or more the second sensor devices are configured to collect ambient information which is information around the vehicle, wherein the one or more first sensor devices are connected to the first electronic control unit via a first gateway device, wherein the one or more second sensor devices are connected to the second electronic control unit via a second gateway device, wherein the plurality of electronic control units (50-1, 50-2) includes a mode management unit configured to determine a certain operation mode of a plurality of operation modes, wherein an operation mode defines the electronic control units and the sensors which are used in said certain operation mode, said sensors being used are also referred to as a use target devices, wherein a sleep instruction control unit is configured to select one gateway device from the first gateway device and the second gateway device, for transitioning said selected gateway to a low power state in which a processing capacity is lowered, whereby said selected gateway is selected for transitioning to the low power state if it does not have to relay data from any sensor which is a use target device in the determined certain operation mode, and wherein the mode management unit, when detecting a malfunction of the first electronic control unit, is further configured to determine the certain operation mode to be a first degenerate mode, and when detecting a malfunction of the second electronic control unit, is configured to determine the certain operation mode to be a second degenerate mode, wherein in the first degenerate mode the second group of devices is used and the sleep instruction control unit is configured to transition the first gateway device to a low power state, and wherein in the second degenerate mode the first group of devices is used and the sleep instruction control unit is configured transition the second gateway device to a low power state. a plurality of electronic control units (50-1, 50-2), wherein a first group of devices including a first electronic control unit and one or more first sensor devices, and a second group of devices including a second electronic control unit and one or more second sensor devices are provided, wherein a plurality of sensor devices including the one or more first sensor devices and one or more the second sensor devices are configured to collect ambient information which is information around the vehicle, wherein the one or more first sensor devices are connected to the first electronic control unit via a first gateway device, wherein the one or more second sensor devices are connected to the second electronic control unit via a second gateway device, wherein the plurality of electronic control units (50-1, 50-2) includes a mode management unit configured to determine a certain operation mode of a plurality of operation modes, wherein an operation mode defines the electronic control units and the sensors which are used in said certain operation mode, said sensors being used are also referred to as a use target devices, wherein a sleep instruction control unit is configured to select one gateway device from the first gateway device and the second gateway device, for transitioning said selected gateway to a low power state in which a processing capacity is lowered, whereby said selected gateway is selected for transitioning to the low power state if it does not have to relay data from any sensor which is a use target device in the determined certain operation mode, and wherein the mode management unit, when detecting a malfunction of the first electronic control unit, is further configured to determine the certain operation mode to be a first degenerate mode, and when detecting a malfunction of the second electronic control unit, is configured to determine the certain operation mode to be a second degenerate mode, wherein in the first degenerate mode the second group of devices is used and the sleep instruction control unit is configured to transition the first gateway device to a low power state, and wherein