An audio operating unit of an audio apparatus is used for speech recognition. Specifically, when it is determined that a speech recognition start switch has been pressed, a speech recognition apparatus outputs a signal indicating volume down to a mute level to an audio-apparatus main body of the audio apparatus via an in-vehicle LAN. In addition, a signal indicating that speech recognition is in operation is outputted to various ECUs via the in-vehicle LAN so that speech recognition is performed. The audio-apparatus main body that has acquired the signal indicating volume down to a mute level lowers the volume to the mute level, while ignoring an output signal from the audio operating unit. On the other hand, the speech recognition apparatus executes a process related to speech recognition by, e.g., selecting or determining one of candidate words based on the output signal from the audio operating unit.