PROBLEM TO BE SOLVED: To provide a holder inserting type non-contact card system capable of easily controlling the resonance frequency of a reader/writer or controlling it in a state close to a practical using state and maximizing communication efficiency independently of the number of non-contact cards. SOLUTION: Since a reader/writer cover 4 is provided with a resonance coil 8a for a transmitting coil, a resonance frequency controlling capacitor 8b for the transmitting coil, a resonance coil 9a for a receiving coil, and a resonance frequency controlling capacitor 9b for the receiving coil and other circuits are not included in the cover 4, the resonance frequency can easily be controlled without requiring the decomposition of a reader/writer body 3 at the time of controlling the resonance frequency and the reduction of communication efficiency due to the shift of the resonance frequency can be prevented.