A vehicle-to-vehicle communication apparatus mounted on a host vehicle, comprising: a host vehicle information storage unit configured to store vehicle information of the host vehicle including vehicle width information related to vehicle width of the host vehicle and location information related to a location of the host vehicle; a receiver capable of performing vehicle-to-vehicle communication and configured to receive vehicle information from a transmitter (163a, 163b, 163c, 163e) of at least a client vehicle (102, 103, 104, 106) capable of performing vehicle-to-vehicle communication, the vehicle information of the at least one client vehicle (102, 103, 104, 106) including vehicle width information related to vehicle width of the at least one client vehicle (102, 103, 104, 106) and location information related to a location information of the at least one client vehicle (102, 103, 104, 106): a provisional information generator, adapted to, upon determination that at least one of the host vehicle and the client vehicles (102, 103, 104, 106)running on any lane of the same running direction as the host vehicle include narrow vehicles (1, 102, 103), being leaning vehicles, each of which is narrower in vehicle width than a wide vehicle having a wide vehicle width and a region formed by connecting said narrow vehicles (1, 102, 103), which are included in the at least one of the host vehicle and the client vehicles (102, 103, 104, 106)running on any lane of the same running direction as the host vehicle, with one another does not include a wide vehicle, based on sets of vehicle information consisting of (a) the vehicle information of at least one of the client vehicles (102, 103, 104, 106) received from the at least one of the client vehicles (102, 103, 104, 106) and the vehicle information of the host vehicle or (b) the vehicle information of at least two of the client vehicles (102, 103, 104, 106) received from the at least two of the client vehicles (102, 103, 104, 106), the provisional information generator is adapted to regard the narrow vehicles (1, 102, 103) as a single provisional vehicle, and generating provisional information of the provisional vehicle from the sets of the vehicle information of the narrow vehicles (1, 102, 103) regarded as the provisional vehicle; and an output controller configured to output the provisional information to a transmitter (163a, 163b, 163c, 163e), a display, a notification unit or a controller. a host vehicle information storage unit configured to store vehicle information of the host vehicle including vehicle width information related to vehicle width of the host vehicle and location information related to a location of the host vehicle; a receiver capable of performing vehicle-to-vehicle communication and configured to receive vehicle information from a transmitter (163a, 163b, 163c, 163e) of at least a client vehicle (102, 103, 104, 106) capable of performing vehicle-to-vehicle communication, the vehicle information of the at least one client vehicle (102, 103, 104, 106) including vehicle width information related to vehicle width of the at least one client vehicle (102, 103, 104, 106) and location information related to a location information of the at least one client vehicle (102, 103, 104, 106): a provisional information generator, adapted to, upon determination that at least one of the host vehicle and the client vehicles (102, 103, 104, 106)running on any lane of the same running direction as the host vehicle include narrow vehicles (1, 102, 103), being leaning vehicles, each of which is narrower in vehicle width than a wide vehicle having a wide vehicle width and a region formed by connecting said narrow vehicles (1, 102, 103), which are included in the at least one of the host vehicle and the client vehicles (102, 103, 104, 106)running on any lane of the same running direction as the host vehicle, with one another does not include a wide vehicle, based on sets of vehicle information consisting of (a) the vehicle information of at least one of the client vehicles (102, 103, 104, 106) received from the at least one of the client vehicles (102, 103, 104, 106) and the vehicle information of the host vehicle or (b) the vehicle information of at least two of the client vehicles (102, 103, 104, 106) received from the at least two of the client vehicles (102, 103, 104, 106), the provisional information generator is adapted to regard the narrow vehicles (1, 102, 103) as a single provisional vehicle, and generating provisional information of the provisional vehicle from the sets of the vehicle information of the narrow vehicles (1, 102, 103) regarded as the provisional vehicle; and an output controller configured to output the provisional information to a transmitter (163a, 163b, 163c, 163e), a display, a notification unit or a controller.