PURPOSE: To eliminate booster circuit for charging a battery by charging the battery with the output voltage, itself, of an external power supply for driving a battery drive data processor body.

CONSTITUTION: When a processor body 4 is driven with a battery, six batteries 1 are connected in series and discharged at a voltage of 6V. When the battery 1 is charged, switches 2, 3 are switched to connect two series of three batteries 1 in parallel so that the batter 1 can be charged with the output voltage 6V of an external power supply 6 which feeds a voltage for driving the processor body 4 directly. Since a 12V power supply for charging six batteries 1 connected in series is not required, the power supply circuit is simplified resulting in the enhancement of power supply efficiency of the processor body, space saving of the charging circuit, and enhancement of portability.