The invention provides a new method to supply a power to a device which is used by connecting to a mobile terminal. The invention also provides a connective device which is connected and enables the mobile terminal to reproduce contents such as music on the mobile terminal. The connective device stores unique identifying information and is detachably connected to the mobile terminal provided with a communication function. The connective device is having a plug terminal connected to an earphone socket of the mobile terminal, and the plug terminal acquires a power from an audio output channel of the earphone socket and output the identifying information via a microphone channel of the earphone socket.