Portable electronic machine

A portable electronic device embodying the present invention comprises a USB connector, an internal power source, a USB controller to execute data communication processing for data communication with a personal computer connected to the USB connector, a main CPU to execute device operation processing for usual operation of the device. When USB controller executes data communication processing, the device is supplied with power at high voltage from the personal computer through the USB connector. When the main CPU executes device operation processing, the device is supplied with power at low voltage from the internal power source. Accordingly, this makes not only high speed data communication available, but also life of the internal power source prolonged.