An RF reader comprising: a sensor configured to detect magnetic field strength; an antenna configured to generate a magnetic field, the antenna being further configured to communicate with a wireless device that is configured to generate a second magnetic field during communication, and the antenna being an antenna coil including a loop antenna that is wound in a flat, annular spiral; and a notification component configured to notify a positional offset between the antenna and the wireless device based on output signal indicative of the magnetic field strength, wherein the sensor is arranged with respect to the antenna such that an effect of the magnetic field generated by the antenna on the output signal is suppressed; and the notification component is further configured to calculate a positional offset direction of the wireless device with respect to the antenna based on the output signal, the notification component being further configured to notify the positional offset direction of the wireless device; characterized in that the magnetic field generated by the antenna has a larger strength in a second region than in a first region; and the sensor is arranged with respect to the antenna such that detection of the magnetic field strength in the second region is suppressed more than detection of the magnetic field strength in the first region; wherein the sensor includes two magnetic sensors (24a, 24b); and the magnetic sensors (24a, 24b) are respectively disposed at a position where the strength of the magnetic field in part of the first region outside of the antenna coil is detected, and a position where a strength of the magnetic field in part of the second region inside of the antenna coil is detected. a sensor configured to detect magnetic field strength; an antenna configured to generate a magnetic field, the antenna being further configured to communicate with a wireless device that is configured to generate a second magnetic field during communication, and the antenna being an antenna coil including a loop antenna that is wound in a flat, annular spiral; and a notification component configured to notify a positional offset between the antenna and the wireless device based on output signal indicative of the magnetic field strength, wherein the sensor is arranged with respect to the antenna such that an effect of the magnetic field generated by the antenna on the output signal is suppressed; and the notification component is further configured to calculate a positional offset direction of the wireless device with respect to the antenna based on the output signal, the notification component being further configured to notify the positional offset direction of the wireless device; characterized in that the magnetic field generated by the antenna has a larger strength in a second region than in a first region; and the sensor is arranged with respect to the antenna such that detection of the magnetic field strength in the second region is suppressed more than detection of the magnetic field strength in the first region; wherein the sensor includes two magnetic sensors (24a, 24b); and the magnetic sensors (24a, 24b) are respectively disposed at a position where the strength of the magnetic field in part of the first region outside of the antenna coil is detected, and a position where a strength of the magnetic field in part of the second region inside of the antenna coil is detected.