RECEIVER AND TRANSMITTER UNIT

A reception control section obtains the rotation angles of wheel assemblies when receiving transmission data by a reception circuit. The reception control section divides 360°, which is the range of the possible rotation angles of the wheel assembly, into equal parts to obtain angle ranges and assigns each of the obtained rotation angles to one of angle ranges. The reception control section derives the angle range in which the number of times (frequency) the obtained rotation angles are included is a maximum value. The reception control section calculates a reception-side angle difference, which is the difference between the median values of the angle ranges in which the number of times the obtained rotation angle is included is a maximum value. The reception control section associates the ID codes with the wheel assemblies based on the correspondence between the reception-side angle difference and the angle difference between specific angles.