To output, by connecting a portable device to an audio device, a music sound from the audio device at a volume of a level equal to that output from the portable device.

In the audio reproducing device, when a portable device 10 is connected via a cable 30, an audio device 20 inquires about the volume set value of the portable device 10 side. The portable device 10 reads the volume set value corresponding to a volume control signal VOL1 from a volume storage part 17 to transmit it to the audio device 20. The audio device 20 sets, by referring to a volume set table in the volume storage part 29, a volume set value on the audio device 20 side corresponding to the volume set value obtained from the portable device 10, and provides a corresponding volume control signal VOL2 to an amplification part 24. Thus, a music sound is output from the loudspeaker 25 of the audio device 20 at the volume of the level almost equal to that output from the amplification part 13 of the portable device 10.