Abstract: In a ringer unit driving system for driving a ringer unit provided in common to a plurality of channel units, the ringer unit sends a ringing signal to a communications device via one of the channel units. A signaling bit detection unit, which is provided in each of the channel units, detects a signaling bit contained in a received digital signal applied to one of the channel units and generates a detection signal. A ringer provided in the ringer unit generates the ringing signal. A power source supplies the ringer with power. A switch is connected between the ringer and the power source and is connected to the signaling bit detection unit. The switch connects the power source and the ringer to each other only when the signaling bit detection unit generates the detection signal.