To provide a tire condition monitoring system in which while a trigger signal for use in registering identification information is transmitted through wireless communication, an intended wheel-side unit can reliably receive the trigger signal.

A tire condition monitoring system includes a handheld communication terminal 4, wheel-side units 3 disposed in respective tires 6 on wheels 2, and a receiver unit 40 that is installed in a vehicle body of a vehicle 1 and has an inherent ID code registered in the wheel-side units 3. The wheel-side unit 3 includes an NFC tag 14 that acquires the ID code and transmits an ID data signal. The handheld communication terminal 4 includes an NFC reader writer 20 that performs near field communication with the NFC tag 14 and transmits a trigger signal for ID code registration to the NFC tag 14.