To prevent the insertion of an electrode plate group into a battery case in an inclined state or in a deviated state from the central position of the battery case in a process inserting the electrode plate group into the battery case.

A pair of ribs 15a long in the height direction is installed on both surfaces of a battery case partition 4 used in a monoblock lead-acid battery and on the inside of a short side surface 7 of the battery case 13, and a plurality of ribs 15b short in the height direction are installed on the inside of the ribs 15a. Along a pair of ribs 15a, the electrode plate group 12 is inserted into the battery case 13 until the bottom of the electrode plate group 12 contacts with the ribs 15b. The length of the short ribs 15b is specified to 6% or more of the dimension in the height direction of a positive plate 1 constituting the electrode plate group 12.