The present invention relates to a semiconductor integrated-circuit device capable of seamlessly switching a power source obtained by rectifying a carrier wave and an external power source. The semiconductor integrated-circuit device having a non-contact card function and a non-contact reader/writer function includes a rectifier 131 for rectifying a received carrier wave, a serial regulator 132 for obtaining a predetermined voltage from an output voltage of the rectifier 131, and a power-supply control circuit 138 for turning on/off the voltage from a battery 160. In a case where the output voltage of the battery 160 is equal to or higher than a predetermined voltage, the power-supply control circuit 138 selects the voltage of the battery 160 as power required for operation of an IC 300 when a reader/writer mode signal or a card mode signal is received. On the other hand, when the output voltage of the battery 160 is lower than the predetermined voltage, the power-supply control circuit 138 selects the output voltage from the rectifier 131 as power required for operation of the IC 300. The present invention can be applied to a portable terminal, such as a cellular phone.
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