To immediately cope with even the case that batteries runs out of power when a user is away from home and to completely eliminate inconvenience that a portable telephone cannot be used due to the dead batteries.

A regulator for regulating a power supply voltage fed from batteries 3 housed in a battery housing part 4 below a prescribed level and an interface connector 2 for electrically connecting the regulator and an charging circuit built in the portable telephone 11 are provided. An adapter 1 is attached to the portable telephone 11 through the connector 2, and the batteries in the portable telephone 11 can be charged by utilizing the power supply voltage of the batteries 3. The portable telephone can easily be charged by the batteries 3 in the adapter 1 by simply attaching the adapter to the portable telephone 11, even when the batteries of the portable telephone 11 runs out of power when the user stays away from home. Since batteries 3 can easily be obtained, there is no problem even though the batteries suddenly runs out of power.