PROBLEM TO BE SOLVED: To reduce the time and labor of inputting an identification number every time of mounting an IC card. SOLUTION: This IC card reader-writer is provided with an input number preservation memory 13 for storing an inputted identification number, an IC card detection part 23 for detecting whether or not the IC card is mounted and a CPU 12 for retrieving whether or not the identification number is stored in the input number preservation memory 13 when the mounting of the IC card 30 is detected. When the identification number is stored in the input number preservation memory 13, the input identification number is transmitted to the IC card 30. Then, it is compared with the identification number stored in the authentication identification number preservation memory 33 of the IC card 30, and when both numbers match, access with the IC card 30 is started.