A wireless tag system comprising two or more wireless communication devices (30, 40) which are enabled to wirelessly communicate with a wireless tag placed in a communication area physically defined, comprising: a box providing an opening, the box comprising an outer box disabling passage of radio waves therethrough and an inner box held in the outer box with a gap left between both an inner surface (21e, 21b, 21c) of the outer box and an outer surface (22e, 22b, 22c) of the inner box, the inner box enabling passage of the radio waves therethrough, the communication area being defined as an internal space of the inner box, the wireless tag being placed in the communication aera; and two or more wireless communication devices (30, 40) including a first wireless communication device and a second wireless communication device, the first wireless communication device having an antenna (32, 32a, 32b), the second wireless communication device having an antenna (42, 42a, 42b), the antennas of both the first and second wireless communication devices (30, 40) being arranged in the gap between the outer and inner boxes (21, 22), wherein the first and second wireless communication devices (30, 40) are adapted to transmit radio waves, serving as transmission waves, on mutually different channels (23CH, 32CH: S11 in Fig. 15) and adapted to simultaneously transmit the transmission waves towards the communication area for a predetermined period of time or a period of time larger than the predetermined period of time, the different channels (23CH, 32CH) being separated from each other in a frequency band by a predetermined frequency or a frequency higher than the predetermined frequency and having no interference in the transmission waves between different channels (23CH, 32CH), the transmission waves transmitted by the two or more wireless communication devices (30, 40) being transmitted into the communication area substantially simultaneously and mutually intensified in the communication area such that electrical power supply to the wireless tag placed within the communication area is stronger than electrical power provided outside the communication area; and the wireless tag is adapted to simultaneously receive the transmission waves transmitted by the first and second wireless communication devices (30, 40). a box providing an opening, the box comprising an outer box disabling passage of radio waves therethrough and an inner box held in the outer box with a gap left between both an inner surface (21e, 21b, 21c) of the outer box and an outer surface (22e, 22b, 22c) of the inner box, the inner box enabling passage of the radio waves therethrough, the communication area being defined as an internal space of the inner box, the wireless tag being placed in the communication aera; and two or more wireless communication devices (30, 40) including a first wireless communication device and a second wireless communication device, the first wireless communication device having an antenna (32, 32a, 32b), the second wireless communication device having an antenna (42, 42a, 42b), the antennas of both the first and second wireless communication devices (30, 40) being arranged in the gap between the outer and inner boxes (21, 22), wherein the first and second wireless communication devices (30, 40) are adapted to transmit radio waves, serving as transmission waves, on mutually different channels (23CH, 32CH: S11 in Fig. 15) and adapted to simultaneously transmit the transmission waves towards the communication area for a predetermined period of time or a period of time larger than the predetermined period of time, the different channels (23CH, 32CH) being separated from each other in a frequency band by a predetermined frequency or a frequency higher than the predetermined frequency and having no interference in the transmission waves between different channels (23CH, 32CH), the transmission waves transmitted by the two or more wireless communication devices (30, 40) being transmitted into the communication area substantially simultaneously and mutually intensified in the communication area such that electrical power supply to the wireless tag placed within the communication area is stronger than electrical power provided outside the communication area; and the wireless tag is adapted to simultaneously receive the transmission waves transmitted by the first and second wireless communication devices (30, 40).