An IC tag reading device is provided that has increased directivity and is capable of determining an accurate position of an IC tag inserted into and placed in a human body even when the operation range of the antenna of the reading device is limited, such as in thoracoscopy, without causing reduction in detectable distance. A reading device antenna for reading an IC tag that has been inserted into a human body and placed at a certain position in order to locate a lesion includes a coil portion having a coil with a predetermined number of turns in a circumferential direction, and a shield portion that covers at least an approximately half of the coil portion in the circumferential direction and causes a bias in a magnetic flux generated from the coil.