A system for controlling vehicle-mounted devices, comprising: a first vehicle-mounted device which is a navigation system comprising a present location detection unit, a storage unit, and a processing unit; wherein the storage unit stores navigation information and programs to be executed by the processing unit and wherein the processing unit is connected to the present location detection unit and the storage unit; a second vehicle-mounted device comprising an hybrid battery and an electric control unit; a further second vehicle-mounted device comprising a motor generator, a power supply circuit, and an electric control unit: a still further second vehicle mounted device comprising an engine and an electric control unit; and a control unit connected to said first vehicle-mounted device and said second vehicle-mounted devices ( 20-1, 20-2, 20-3) wherein said control unit comprises: a signal transmission means that is configured to transmit a predetermined signal to said first vehicle-mounted device; a cooperative control means that is configured to perform cooperative control in which, when said first vehicle-mounted device responds to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled using information used by said first vehicle-mounted device; and an alternative control means that is configured to perform alternative control in which, when said first vehicle-mounted device does not respond to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled without using information used by said first vehicle-mounted device, wherein said first vehicle-mounted device is configured to store information on a downward slope in a driving route of the vehicle in the storage unit and to use said information for controlling said second vehicle-mounted devices ( 20-1, 20-2, 20-3) to reduce a state of charge of said hybrid battery before reaching the downward slope. a first vehicle-mounted device which is a navigation system comprising a present location detection unit, a storage unit, and a processing unit; wherein the storage unit stores navigation information and programs to be executed by the processing unit and wherein the processing unit is connected to the present location detection unit and the storage unit; a second vehicle-mounted device comprising an hybrid battery and an electric control unit; a further second vehicle-mounted device comprising a motor generator, a power supply circuit, and an electric control unit: a still further second vehicle mounted device comprising an engine and an electric control unit; and a control unit connected to said first vehicle-mounted device and said second vehicle-mounted devices ( 20-1, 20-2, 20-3) wherein said control unit comprises: a signal transmission means that is configured to transmit a predetermined signal to said first vehicle-mounted device; a cooperative control means that is configured to perform cooperative control in which, when said first vehicle-mounted device responds to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled using information used by said first vehicle-mounted device; and an alternative control means that is configured to perform alternative control in which, when said first vehicle-mounted device does not respond to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled without using information used by said first vehicle-mounted device, wherein said first vehicle-mounted device is configured to store information on a downward slope in a driving route of the vehicle in the storage unit and to use said information for controlling said second vehicle-mounted devices ( 20-1, 20-2, 20-3) to reduce a state of charge of said hybrid battery before reaching the downward slope. a signal transmission means that is configured to transmit a predetermined signal to said first vehicle-mounted device; a cooperative control means that is configured to perform cooperative control in which, when said first vehicle-mounted device responds to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled using information used by said first vehicle-mounted device; and an alternative control means that is configured to perform alternative control in which, when said first vehicle-mounted device does not respond to the predetermined signal, said second vehicle-mounted devices ( 20-1, 20-2, 20-3) are controlled without using information used by said first vehicle-mounted device, wherein said first vehicle-mounted device is configured to store information on a downward slope in a driving route of the vehicle in the storage unit and to use said information for controlling said second vehicle-mounted devices ( 20-1, 20-2, 20-3) to reduce a state of charge of said hybrid battery before reaching the downward slope.