A battery is charged utilizing electric power provided by a power supply line included in a cable that is in accordance with IEEE 1394. A charging apparatus and a personal computer are connected together by the cable. A power source unit in the personal computer converts AC voltage to direct voltage and supplies the DC voltage to the power supply line. The voltage is applied to a charging circuit via the power supply line, thereby charging the battery. A signal line included in the cable is used when the charging apparatus and personal computer send and receive data to and from each other.