PURPOSE: To simplify remarkably the structure, by containing a solar battery which becomes a main one, and a battery for backup so as to be freely attachable in the same battery chamber, and also constituting so that an output can be fetched selectively from two batteries.

CONSTITUTION: The lower part of a housing 5 is fitted into an opening part 1a in a state that a solar battery 7, a backup battery 8 and a connector 9 are contained in order from the upper part, in the inside of the housing 5. In this case, projections 5b, 5b are fitted into a notch part 1b of the lower part of the side wall of the opening part 1a, are pressed and turned against elastic force of a contact spring 11 by using said part as a supporting point, a selecting switch 3 is slided to the housing 5 side as it remains pressed, and a tip part 3b is fitted into a long hole 5c. In this state, in case when the tip part 3b of the selecting switch 3 is moved to the housing 5 side to the maximum, the backup battery 8 is selected, and when the selecting switch is moved to a position of S, the solar battery 7 is selected.