Chip for noncontact reader/writer having function for managing power supply

A portable terminal device comprising a semiconductor integrated-circuit device including:

• rectifying means for rectifying a received carrier wave;
• generation means for generating a first power-supply voltage on the basis of an output by said rectifying means;
• and
• selection means for selecting one of said first power-supply voltage generated by said generation means and a supplied second power-supply voltage as a power-supply voltage required for operation,
• wherein said selection means selects said first power-supply voltage as a power-supply voltage required for operation when said second power-supply voltage is equal to or lower than a threshold value, and selects said second power-supply voltage as a power-supply voltage required for operation when said second power-supply voltage is equal to or higher than the threshold value and an instruction to operate in accordance with a predetermined function is given.

A settlement method for performing a settlement, which occurs as a result of a predetermined transaction, with a portable terminal device comprising:

• rectifying means for rectifying a received carrier wave;
• generation means for generating a first power-supply voltage on the basis of an output by said rectifying means;
• selection means for selecting one of said first power-supply voltage generated by said generation means and a supplied second power-supply voltage as a power-supply voltage required for operation;
• and storage means for storing money information as a predetermined transaction price, said settlement method comprising:
• a communication step of performing communication with said portable terminal device;
• a reading step of reading said money information stored in said portable terminal device in the process of said communication step;
• and
• a settlement step of performing a settlement on the basis of said money information read in the process of said reading step.