A system for detecting a connection between two devices includes a first device and a second device. The first device includes a first connection terminal and a first reactance element connected to the first connection terminal. The second device includes a second connection terminal; a first resistance element, and a first frequency generator for allowing a signal to pass through the first resistance element and be applied to the first device via the second connection terminal. The second device further includes a first comparator having both input terminals connected to both ends of the first resistance element, and comparing and outputting a signal of both ends of the first resistance element, and a first control unit for determining whether or not the first connection terminal of the first device is connected to the second connection terminal by means of the output signal of the first comparator.