Abstract: A non-contact IC card communication in which power consumption of a driver of a reader/writer is reduced and the size of a power supply circuit for operating the driver is made small. The driver has a low output impedance. A current detecting circuit including a detecting coil magnetically coupled with a transceiver coil of the reader/writer through a magnetic coiling element and a resistor detects a current which flows through the transceiver coil. A voltage drop to be detected is small and is approximately constant for a variation of the transceiver coil current. When data is read from an IC card, a load of the driver is changed. The driver drives the transceiver coil in a constant voltage fashion even if a current flowing through the transceiver coil changes due to the change in load. Input voltages of a rectifying/smoothing circuit and a regulator in the IC card become approximately constant. As a result, the amplitude of a high frequency output voltage of the driver can be made small.

Abstract: System for controlling communication between electronic information cards, such as IC-cards and a host computer, to be kept in secret. In order to protect the data, various countermeasures have been proposed in which the data are enciphered to be sent and deciphered for reading out. There is a problem, however, the cyphograph is difficult to keep secret when it is used for a long time. The invention intends to provide a device having at least two connectors for an IC-card stored with an algorithm for enciphering the data and another IC-card or other IC-cards for making communication with the host computer so as to readily change the first IC-card with a new one storing another algorithm.