| 摘要 |
First and second antennas (1, 2) are arranged such that a distance between a wireless tag (8) and the first antenna (1) is shorter than that between the wireless tag (8) and the second antenna (2). A judging section (5) is provided for judging whether communication is normal or not, based on a difference between a reception level value of radio waves received by the first antenna (1) and a reception level value of radio waves received by the second antenna (2). Thus, abnormal communication made from a remote place by a malicious third party is judged. |
