PURPOSE: To simply execute the attaching/detaching operation of a battery pack to/from a portable telephone set body.

CONSTITUTION: A latch mechanism part 4 having a hook 41 to be alternately set up to an upper part and a lower part in each depression is fixed to the rear end side of a battery pack storing part 2 in a portable telephone set body 1 and a locking recessed part 6 to be locked with a locking projected part 7 of a battery pack 3 is formed on the head side of the storing part 2. In the case of loading the pack 3, the projected part 7 of the pack 3 is engaged with the recessed part 6 of the storing part 2 and the rear end side of the pack 3 is depressed. When an locking groove 5 of the pack 3 depresses the hook 41, the hook 41 is engaged with the gloove 5 and locked on the lower position to store the pack 3 in the storing part 2. Then the pack 3 is fixed through a drop preventing lug 9 formed on the pack 3 by sliding a drop preventing lock part 8 formed on the body 1.