PURPOSE: To make it possible to use two kinds of batteries and to prevent the primary battery from mischarge by forming three or more contacts to be connected to one of a chargeable battery and an unchargeable battery and contacts for a reverse current preventing diode and charging.

CONSTITUTION: A nickel-cadmium battery 22 is stored in its storage case 21 and the plus and minus sides are connected to contacts (b) and (a) respectively. An alkaline mangan battery 20 is stored in its storage case 19 and the plus and minus sides are connected to contacts (c) and (a) respectively. In case of using the battery 22, the case 21 is connected to the contacts 17a, 17b of a device body 13 to supply electric power directly to a power supply part 14. When a battery voltage is dropped, the battery 22 is connected so that the body 13 is charged from a charging port 12. In case of using the battery 20, the case 19 is connected to the contacts 17a, 17b of the body 13 and the applied voltage is converted into 5V by a voltage converting circuit 16 and supplied to the power supply part 14. Even if an operator inserts a charging plug into the charging port 12 in error, the battery 20 is not charged because of the existence of the charge preventing diode 15.