A data processing apparatus and card-sized data processing device that consume less power and operate more reliably. An antenna captures a radio wave sent from an external reader/writer device, and a receiver converts it into an electrical signal. From this electrical signal, a first power supply circuit produces a first supply voltage for use in analog circuits. A second power supply circuit produces a second supply voltage that is different from the first supply voltage, for use in memory circuits. A third power supply circuit produces a third supply voltage that is different from the other voltages, for use in digital circuits. The memory and digital circuits thus operate with different supply voltages optimized for their individual requirements. Total power consumption of the device is reduced by lowering the voltage for the digital circuits, including MPU, while giving a higher voltage to the memory circuits.