A plurality of terminal devices, e.g., game apparatuses 2 are interconnected to each other through a network 4. The respective game apparatuses 2 receive signals inputted from the outside, e.g., television signals broadcast from a broadcasting antenna and extract synchronizing signals from the broadcasting signals. Based on the extracted synchronizing signals, the respective game apparatuses 2 make synchronization control of operations, data communication among the respective game apparatuses 2. The respective game apparatuses 2 use the common signals to make the synchronization control, whereby the respective game apparatuses 2 can be synchronized with one another suitably without timing shift. The terminal devices synchronizing method can suitably synchronize timings of communication among a plurality of terminal devices.