The invention provides a tag communication system, an interference preventing method and a tag communication controller suitable for prevention of a radio wave interference able to be caused by radio waves mutually emitted when plural tag communication devices are arranged. Plural reader-writers are oppositely arranged through a belt conveyer for conveying an article. A null of the reader-writer is opposed to a null of the reader-writer. A null of the reader-writer is opposed to a null of the reader-writer. Main lobes are directed to a direction causing no mutual interference.