The present invention is related to a vehicle-mounted multimedia apparatus 1 which has at least one functional module 42A, 42B, 42C . . . 42N which is powered from a power source 50 to operate and an interface 12 to which an extension device 20 is to be connected. When the extension device 20 is newly connected to the interface 12, if there is an existing functional module 42B (referred to as a corresponding functional module), which corresponds to a functional module 22 provided in the extension device 20, among the existing functional module 42A, 42B, 42C . . . and/or 42N which already exists in a state before said connection of the extension device, said vehicle-mounted multimedia apparatus 1 stops powering the corresponding functional module 42B and powers the functional module 22 provided in the extension device 20.