In a tire air pressure detection system, a trigger device is caused to transmit a notification trigger signal to notify wheel position detection in advance of outputting a detection trigger signal for signal magnitude measurement. After confirming reception of the notification trigger signal by a transceiver device, the trigger device is caused to transmit a detection trigger signal for wheel position detection. The detection trigger signal is transmitted after the transceiver device is set in a signal reception wait condition. The transceiver device is thus enabled to receive the detection trigger signal to measure a signal magnitude of the detection trigger signal.