To reduce the number of wiring for controlling sound volume and to hardly mix noise.

A sound volume varying device is provided with a digital attenuator 5 provided inside a digital signal processor 3 and an analog attenuator 7 provided outside. After the digital attenuator 5 attenuates an inputted audio signal for instructed attenuation quantity, the analog attenuator 7 further attenuates that signal for designated attenuation quantity and outputs it. Based on sound volume data instructed from an external controller 11, an attenuation quantity control part 12 inside the digital signal processor 3 performs the fine adjustment of volume by controlling the attenuation quantity of digital attenuator 5. Besides, based on these data, the attenuation quantity control part 12 performs the main adjustment of volume by controlling the attenuation quantity of analog attenuator 7. The number of control lines 13 for connecting the analog attenuator 7 with the attenuation quantity control part 12 is set corresponding to the number of attenuation quantity settable for the analog attenuator 7.