The present invention simplifies locking of a battery pack (12) within a cell-phone lower case (13). A battery lock member (50) has a first inclined surface that permits sliding of the battery lock member (50) in such a way that an operation of housing the battery pack (12) in the battery pack housing (33) causes an engagement protrusion (32), which is formed to protrude from a side face of the battery pack (12), to slide in contact with the first inclined surface, thereby releasing the locking, and a second inclined surface that permits sliding of the battery lock member (50) in such a way that an operation of attaching a battery lid (11) to a battery lid holder (43) causes a depression protrusion (31), which is formed to protrude from the bottom face of the battery lid (11), to slide in contact with the second inclined surface, thereby achieving the locking.