A master terminal transmits sound waves that are a synchronization signal from a speaker to a slave terminal at random time intervals. Upon acquiring the sound waves that are the synchronization signal by microphone, the slave terminal promptly transmits a response signal through wireless communication to the master terminal. The master terminal receives the response signal and a terminal ID transmitted from the slave terminal. The master terminal receives the response signal multiple times and determines whether time intervals when synchronization signals were transmitted and time intervals when response signals were received match. When the synchronization signal time intervals and the response signal time intervals match, the master terminal recognizes the slave terminal that transmitted response signals at time intervals matching the synchronization signal time intervals as a wireless communication connection target. Slave terminals that transmitted response signals at time intervals not matching the synchronization signal time intervals are excluded from wireless communication connection targets.