An expansion device connected to a host device to thereby expand the functions
thereof. Even when source power is not supplied from the host device, this expansion
device, such as a bay unit, enables reproduction of an audio disk inserted thereinto.
The bay unit used by being connected to the host device, in a state in which a
recording/reproducing device capable of reproducing digital signals and audio signals
is accommodated in a bay, has an operation panel for operating the recording/reproducing
device, an audio circuit, which includes an amplifying circuit, a speaker, and
a volume control, and a second power input portion to be connected to an existing
power supply circuit. Further, source power is supplied thereto from the second
power input portion. This enables the recording/reproducing device and the audio
circuit to operate even when no source power is supplied from the existing power
supply circuit, for example, when the power supply for the host device is turned
off, and when the bay unit is disconnected from the host device. A battery incorporated
in the bay unit may be connected to the second power input portion.
