To reduce the vexatious complication of personal authentication when using an information technology device or a card, a combination of RFID tags worn by a user is stored when personal authentication is carried out. After that, the RFID tags are detected again in a situation where personal authentication is required. The continuous use of the previous personal authentication is permitted depending on the extent of coincidence between pieces of RFID information thus detected and the combination of stored RFID information, so that further authentication operations can be omitted. In addition, reference is made to a past archive when an RFID list is created. A weighted coefficient is then calculated based on the put-on frequency (put-on archive) in terms of a user's single article or a combination of such articles. The utilization of the weighted coefficient provides personal authentication with a high level of reliability.