An information management system comprising an IC tag (112-1) for RFID for storing information related to an article (131-1) which is to be managed, a communication sheet structure , and a transmission/reception unit which transmits electromagnetic waves toward said communication sheet structure and receives signals from said IC tag through said communication sheet structure, wherein the communication sheet structure comprises at least three layers including a conductor layer A , a base member layer and a conductor layer B described below, which are laminated in order, wherein the size of said communication sheet structure in the direction of width thereof at right angles with the direction in which the transmitted electromagnetic waves travel in a plane thereof is nearly equal to a natural number of times of one-half the wavelength of said transmitted electromagnetic waves so as to establish a resonating state in said direction of width: conductor layer A : a layer in which continuous, conducting portions A and nonconducting portions A are present, said conducting portions A having an electric resistance of not larger than 1 Ω/□; base member layer : a layer of a resin molded body or a fiber structure having a relative dielectric constant of 1.0 to 5.0 at a frequency of 800 MH Z to 10 GH Z ; conductor layer B : a layer in which a conducting portion B is a present over not less than 90% of the area thereof, said conducting portion B having an electric resistance of not larger than 1 Ω/□. an IC tag (112-1) for RFID for storing information related to an article (131-1) which is to be managed, a communication sheet structure , and a transmission/reception unit which transmits electromagnetic waves toward said communication sheet structure and receives signals from said IC tag through said communication sheet structure, wherein the communication sheet structure comprises at least three layers including a conductor layer A , a base member layer and a conductor layer B described below, which are laminated in order, wherein the size of said communication sheet structure in the direction of width thereof at right angles with the direction in which the transmitted electromagnetic waves travel in a plane thereof is nearly equal to a natural number of times of one-half the wavelength of said transmitted electromagnetic waves so as to establish a resonating state in said direction of width: conductor layer A : a layer in which continuous, conducting portions A and nonconducting portions A are present, said conducting portions A having an electric resistance of not larger than 1 Ω/□; base member layer : a layer of a resin molded body or a fiber structure having a relative dielectric constant of 1.0 to 5.0 at a frequency of 800 MH Z to 10 GH Z ; conductor layer B : a layer in which a conducting portion B is a present over not less than 90% of the area thereof, said conducting portion B having an electric resistance of not larger than 1 Ω/□. conductor layer A : a layer in which continuous, conducting portions A and nonconducting portions A are present, said conducting portions A having an electric resistance of not larger than 1 Ω/□; base member layer : a layer of a resin molded body or a fiber structure having a relative dielectric constant of 1.0 to 5.0 at a frequency of 800 MH Z to 10 GH Z ; conductor layer B : a layer in which a conducting portion B is a present over not less than 90% of the area thereof, said conducting portion B having an electric resistance of not larger than 1 Ω/□. <EOS>