A relaying device for providing optimum communication between a non-contact information medium and an information read/write device, and a communication system employing the relaying device, in which the adverse effect on communication, brought about by limitations on the mounting site of the information read/write device may be eliminated. The relaying device is formed by a resonance circuit 34 including a first antenna coil 31, electro-magnetically coupled to an antenna coil 11 of the information read/write device 10, a second antenna coil 32, connected in series with the first antenna coil 31 and electro-magnetically coupled to an antenna coil 21 of the non-contact information medium 20, and a tuning capacitor 33 connected in series with the first antenna coil 31 and the second antenna coil 32. The first antenna coil 31, second antenna coil 32 and the tuning capacitor 33 making up the resonance circuit 34 is resonated with the same resonance frequency as that of the resonance circuit 13 of the information read/write device 10 and that of the resonance circuit 23 of the non-contact information medium 20.