To make a voice guidance related to an ETC audible even if an audio signal is reproduced from an audio device arranged in an automobile when a voice guidance signal for guiding the automobile to a specific lane is output in the electronic toll collection system based on signal transmission between an automatic toll collecting device on a turnpike and an on-vehicle ETC device.

The audio device 19 is provided with a voice information storage part 51 storing the voice guidance related to the ETC and a power source control part 92 turning on a power source for the audio device 19 according to a signal from the ETC device 100. On the basis of the signal from the ETC device 100, voice information to be reproduced is selected while a signal of a radio set or music reproducing media in the audio device 19 is cut off, and the voice guidance is outputted from the audio device 19 without respect to turning on/off of the power source.