To make it possible to miniaturize an external power supply with a function of charging an internal battery maintained, by controlling a changing circuit according to the presence or absence of connection with an external power supply and the state of the operation of electronic equipment.

A system-off signal generated by a power switch 9 is supplied to a power supply control circuit 1, and the power supply control circuit 1 sends a control signal to a constant voltage control circuit 5. The constant voltage control circuit 5 turns off a constant voltage circuit 6 (charging circuit 4), and a system 7 is thereby turned off. Thereafter, the power supply control circuit 1 sends a control signal to a charge control circuit 3, and the charge control circuit 3 turns off the charging circuit 4 to charge a battery 8. Thereby, an external power supply of small power capacity can be used with a charging function maintained, and thus the external power supply can be miniaturized in electronic equipment.