A system comprising: a plurality of readers (101-103); and an information processor , characterized in that each reader (101-103) includes: a first communicator configured to communicate with the information processor , an antenna configured to communicate with radio tags, and a first processor configured to measure a time and an intensity value of the radio waves in which radio waves are received with a plurality of channels in a carrier sense time, the carrier sense time being a time in which the radio tags are not communicating with one of the plurality of readers (101-103), and to transmit a channel report indicating a time in which radio waves are received with each channel and an intensity value of the radio wave received in the carrier sense time to the information processor through the first communicator , and wherein the information processor includes: a second communicator configured to communicate with the plurality of readers (101-103), and a second processor configured to acquire the channel report from each of the plurality of readers (101-103) through the second communicator and to generate an aggregate report indicating channel states while one of the plurality of readers (101-103) is not communicating with the radio tags based on the plurality of acquired channel reports. a plurality of readers (101-103); and an information processor , characterized in that each reader (101-103) includes: a first communicator configured to communicate with the information processor , an antenna configured to communicate with radio tags, and a first processor configured to measure a time and an intensity value of the radio waves in which radio waves are received with a plurality of channels in a carrier sense time, the carrier sense time being a time in which the radio tags are not communicating with one of the plurality of readers (101-103), and to transmit a channel report indicating a time in which radio waves are received with each channel and an intensity value of the radio wave received in the carrier sense time to the information processor through the first communicator , and a first communicator configured to communicate with the information processor , an antenna configured to communicate with radio tags, and a first processor configured to measure a time and an intensity value of the radio waves in which radio waves are received with a plurality of channels in a carrier sense time, the carrier sense time being a time in which the radio tags are not communicating with one of the plurality of readers (101-103), and to transmit a channel report indicating a time in which radio waves are received with each channel and an intensity value of the radio wave received in the carrier sense time to the information processor through the first communicator , and wherein the information processor includes: a second communicator configured to communicate with the plurality of readers (101-103), and a second processor configured to acquire the channel report from each of the plurality of readers (101-103) through the second communicator and to generate an aggregate report indicating channel states while one of the plurality of readers (101-103) is not communicating with the radio tags based on the plurality of acquired channel reports. a second communicator configured to communicate with the plurality of readers (101-103), and a second processor configured to acquire the channel report from each of the plurality of readers (101-103) through the second communicator and to generate an aggregate report indicating channel states while one of the plurality of readers (101-103) is not communicating with the radio tags based on the plurality of acquired channel reports. <EOS>