Patent ID: 7243855

Claim:
A contactless identification tag that sets a time slot number concerning a sequence of communications with a reader/writer device at the time of data communications with the reader/writer device by a time-division multiplex method using a plurality of time slots, and is capable of radio communications in a contactless manner with the reader/writer device according to a sequence of communications that is decided based on the time slot number that has been set, the contactless identification tag comprising: identification number storage means for storing a unique identification number; random number generator means for generating a random number; and time slot number setting means for setting the time slot number based on the identification number and the random number, wherein the random number and a bit position in a bit string indicating the identification number are correlated with each other in advance, and wherein the time slot number setting means extracts a numerical value at the bit position corresponding to the random number from the bit string indicating the identification number, and sets the time slot number based on the extracted numerical value.