A mobile apparatus is provided with a first charging circuit, and a charging device is provided with a second charging circuit. The charging device charges a secondary buttery of the mobile apparatus through three pairs of terminals, that is, the first input/output terminals of DC voltage, second input/output terminals of a charging voltage, and third input/output terminals connected to ground. With this arrangement, an effective charging operation is executed with minimum loss. Since the secondary buttery is charged only when the mobile apparatus is installed on the charging device and a power switch of the mobile apparatus is turned off, data stored in the mobile apparatus can be protected against destruction and the secondary buttery can be charged in safety.