PURPOSE: To facilitate removal/mounting work of combinedly cells, to improve working efficiency and to enhance reliability by fitting the cells for back-up power supply of LCD, etc., to the rear surface of an operation part lid which seals an operation opening of a storage case.

CONSTITUTION: A see-through window 7a and an operation opening are provided in the surface of a cover part 7 forming a storage case. Then, since a fitting position of cells 16 is the rear surface of an operation part lid 10, the cells 16 is replaced in the following procedure. First, the operation part lid 10 is released for releasing the connection of a connector 15 and then mounting screws 17 are loosened for removing the old cells. New cells is set in the reverse order, thus facilitating replacement operation. Also, the edge part of the rear surface of the operation part lid 10 protrudes and the inside is in recessed shape so that the cells 16 which is fitted to the recessed part can fully utilize a space, thus eliminating the need for a space for the cells 16 at the storage case.