An electronic apparatus has a stand-by mode. The electronic apparatus includes a first circuit, a second circuit and a third circuit. The first circuit has an interface and transfers data to an external device. The second circuit has a processor and sets a first power supplying mode of the first circuit. The third circuit sets a second circuit power supplying mode of the second circuit and sets a second power supply mode of the first circuit when the second circuit is disabled. The processor selects a first circuit power supplying mode from power supplying modes of the first circuit as the second power supplying mode before the second circuit is disabled.