This invention relates to a cellular radio telephone set having a USB
peripheral circuit which realizes a USB connection function. When the
cellular radio telephone set is connected to an information processing
terminal apparatus via a USB cable, a voltage Vbus supplied from the
information processing terminal apparatus is regulated and supplied to
the USB peripheral circuit. When the cellular radio telephone set is not
connected to the information processing terminal apparatus via the USB
cable, an application CPU which controls the USB peripheral circuit is
shifted to a sleep mode.