An in-vehicle network system comprising: an upper device; a first intermediate unit (21; 23) that is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using a first communication system; a second intermediate unit (22; 24) that is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using a second communication system; and a lower unit (31; 32, 33) that is connected to the first intermediate unit and the second intermediate unit and is configured to communicate with the first intermediate unit using the first communication system and communicate with the second intermediate unit using the second communication system characterised in that: the in-vehicle network system includes a plurality of the first intermediate units (21, 23) and a plurality of the second intermediate units (22, 24); one of the first intermediate units is disposed in any one of four sections of a vehicle, the four sections being a right front section, a left front section, a right rear section, and a left rear section that are divided about a position in the vehicle at which the upper device is disposed; another one of the first intermediate units in the section that is diagonal to the one of the sections; each of the first intermediate units disposed in the one of the section and the section that is diagonal to the one of the section is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using the first communication system; one of the second intermediate units is disposed in the section that is adjacent to the one of the sections in a front-rear direction; another one of the second intermediate units is disposed in the section that is adjacent to the one of the sections in a right-left direction; and each of the second intermediate units disposed in the sections that are adjacent to the one of the sections in the front-rear direction and the right-left direction respectively is connected to the upper device directly or via at least one device, and is configured to communicate using the second communication system. an upper device; a first intermediate unit (21; 23) that is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using a first communication system; a second intermediate unit (22; 24) that is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using a second communication system; and the in-vehicle network system includes a plurality of the first intermediate units (21, 23) and a plurality of the second intermediate units (22, 24); one of the first intermediate units is disposed in any one of four sections of a vehicle, the four sections being a right front section, a left front section, a right rear section, and a left rear section that are divided about a position in the vehicle at which the upper device is disposed; another one of the first intermediate units in the section that is diagonal to the one of the sections; each of the first intermediate units disposed in the one of the section and the section that is diagonal to the one of the section is connected to the upper device directly or via at least one device and is configured to communicate with the upper device using the first communication system; one of the second intermediate units is disposed in the section that is adjacent to the one of the sections in a front-rear direction; another one of the second intermediate units is disposed in the section that is adjacent to the one of the sections in a right-left direction; and each of the second intermediate units disposed in the sections that are adjacent to the one of the sections in the front-rear direction and the right-left direction respectively is connected to the upper device directly or via at least one device, and is configured to communicate using the second communication system.