This study developed a digital security device which power is on/off by the RFID card. This device is based on the wireless data transmit/receive circuits, built in RS-232C chip and applied to computer and other digital devices. We can check whether this device is operated or not by connecting the LED. In this system, 13.56MHz frequency circuit supplies power with ID card, and DC inputs check the proximity operating distance of the card field for verifying the existence of a card. The security level of this system is much stronger than that of a compared system[13]. Anyone cannot use the system without RFID card. All illegal access is prevented except for authorized path.