A receiver configured to be mounted on a vehicle having rotation angle detecting sections each of which detects a rotation angle of one of wheel assemblies , wherein a transmitter is attached to each wheel assembly , the receiver being configured to identify the wheel assembly to which each transmitter is attached, the receiver comprising: a receiving section , an obtaining section configured to obtain the rotation angle from the rotation angle detecting section upon reception of the transmission data by the receiving section ; a calculation section configured to calculate a difference between the rotation angle obtained by the obtaining section and a previously obtained rotation angle; and an identifying section configured to determine whether the difference calculated by the calculation section is included in a predetermined range and associates an ID code included in the transmission data with the wheel assembly , wherein the range includes a reference range that includes 0, characterized in that the receiving section is configured to receive transmission data that is transmitted from each transmitter when the transmitter detects that the associated wheel assembly is at each of different specific angles set in possible rotation angles of the wheel assembly ; and the identifying section is configured to associate the ID code with the wheel assembly based on the number of times the difference is included in the range, wherein the range includes a specific range that includes an angle difference between different specific angles, wherein the angle difference varies among the transmitters , and the receiver further comprises a reception storage section that stores the ID codes of the transmitters while associating the ID codes with the specific range. a receiving section , an obtaining section configured to obtain the rotation angle from the rotation angle detecting section upon reception of the transmission data by the receiving section ; a calculation section configured to calculate a difference between the rotation angle obtained by the obtaining section and a previously obtained rotation angle; and an identifying section configured to determine whether the difference calculated by the calculation section is included in a predetermined range and associates an ID code included in the transmission data with the wheel assembly , wherein the range includes a reference range that includes 0, the receiving section is configured to receive transmission data that is transmitted from each transmitter when the transmitter detects that the associated wheel assembly is at each of different specific angles set in possible rotation angles of the wheel assembly ; and the identifying section is configured to associate the ID code with the wheel assembly based on the number of times the difference is included in the range, wherein the range includes a specific range that includes an angle difference between different specific angles, wherein the angle difference varies among the transmitters , and the receiver further comprises a reception storage section that stores the ID codes of the transmitters while associating the ID codes with the specific range. <EOS>