A network system includes at least one transmission path and a plurality of terminal devices each connected to the transmission path. Each of the terminal devices includes a transceiver, a startup processing unit, and a switching unit. The transceiver is configured to operate either one of a first standby unit and a second standby unit according to a switching instruction. The switching unit is configured to output the switching instruction to the transceiver to operate the second standby unit when a transmission path empty period lasts for a predetermined preparation time or more after a non-designation period has lasted for a predetermined operation determination time or more.