PURPOSE: To improve lead wire connection workability and easily and surely carry out soldering by making it unnecessary to wind and solder a core wire of a lead wire to a battery's terminal.

CONSTITUTION: The projected lengths of battery terminal straight parts 24b-27b projected out of a through hole 21a of a battery box part 21 are made almost the same. A relay substrate 30 having slits 30a1-30d1 to be joined with the straight parts 24b-27b from side is provided. Connection terminal parts 34a-34d are formed in the parts facing to the respective slits 30a1-30d1 of the relay substrate 30. Holding holes 30e1, 30f1 are held in holding hooks 21c, 21d of the battery box part 21 to stably fix the relay substrate 30 in the battery box part 21 and at the same time the slits 30a1-30d1 are connected with the straight parts 24b-27b. Finally, soldering 38 is carried out between the straight parts 24b-27d and the connection terminal parts 34a-34d.