A tag reading apparatus comprises a passage that is configured to receive an RFID-tagged article that is to be registered in a transaction. The passage has an inlet end and an outlet end separated from each other in a first direction and width in a second direction. An antenna is in the passage at a position between the inlet and outlet ends in the first direction. An RFID reader is provided to read an RFID tag according to a response wave from the RFID tag received via the antenna. A controller is configured to identify the RFID-tagged article as being in the transaction according to a change in the response wave (such as a phase difference or intensity) corresponding to a movement of the RFID-tagged article from the inlet end to the outlet end.