Abstract: In the inventory management system managing the inventory status of a commodity displayed in a showcase by using a computer, the showcase is provided with an antenna for communicating with an RFID tag attached to a commodity on a commodity shelf, detecting means for detecting a unique number of the RFID tag by communicating with the RFID tag through the antenna, and transmitting means for transmitting the detected unique number of the RFID tag to the computer through a network. The computer manages the commodity inventory based on the unique number of the RFID tag, the unique number being received from the showcase.

Abstract: A control unit of a reader superimposes a control signal for antenna switching on a high frequency signal outputted into an antenna unit from a high frequency circuit. The antenna unit includes: separators for separating the superimposed signals into high frequency signals and control signals; a switch circuit for switching loop antennas; and a control circuit for controlling the switch circuit based on the control signal separated by the separator.

Abstract: An RFID tag reader having an antenna for communication with an RFID tag, a high frequency circuit for processing a communication signal with the RFID tag, a signal line for connecting the antenna with the high frequency circuit, and an impedance matching circuit for impedance matching between the antenna and the signal line includes: a detection unit for detecting a calibration RFID tag provided in a predetermined reading range; and a calibration unit for calibrating the high frequency circuit or matching circuit so that the calibration RFID tag can be detected by the detection unit.

Abstract: A control unit of a reader superimposes a control signal for impedance adjustment on a high-frequency signal outputted from a high-frequency circuit to an antenna unit to output a superimposed signal. The antenna unit includes a separating unit that separates the superimposed signal into the high-frequency signal and the control signal, a matching circuit that subjects the high-frequency signal separated by the separating unit to impedance matching and input the high-frequency signal to an antenna, and an adjusting unit that controls a circuit constant of the matching circuit on the basis of the control signal separated by the separating unit.