A system includes a plurality of readers and an information processor. The reader includes a first communicator, an antenna, and a first processor. An antenna communicates with radio tags. The first processor measures a time 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 and transmits a channel report indicating a time in which radio waves are received with each channel to the information processor through the first communicator. The information processor includes a second communicator and a second processor. The second processor acquires the channel report through the second communicator and generates an aggregate report indicating channel states while the plurality of readers are not communicating with the radio tags based on the plurality of acquired channel reports.