Radio-frequency tag communication system and radio-frequency tag communication device, which permit highly efficient coordinated operations of the communication devices while preventing overlapping of communication. The communication system includes a positional-relationship determining portion configured to determine relative positions of the plurality of radio-frequency tag communication devices, and a transmission control portion configured to control transmission of the transmitted signal from each of the plurality of radio-frequency tag communication devices, according to a result of determination of the relative positions by the positional-relationship determining portion, so that a sufficiently long time is provided for the mutually adjacent communication devices to transmit the transmitted signals. Namely, the present invention provides a radio-frequency tag communication system wherein the radio-frequency tag communication devices are operable in a coordinated fashion with high efficiency, while preventing overlapping of communication.