To obtain a lead-acid battery which can prevent electrolytic solution in an electrolyzer from overflowing out of the liquid port plug by vibration.

In the electrolyzer 1 housing an electrode plate group 2, an electrolytic solution 3 is housed to the top of the electrode plate group 2. A liquid port 6 is installed on a cap 5 occluding the electrolyzer 1, and this liquid port 6 is occluded with a liquid port plug 7. In the electrolyzer 1, a liquid level behavior inhibition fixture 8 to restrain the liquid level behavior of the electrolytic solution 3 is arranged so that the upper part should be on the liquid level of the electrolytic solution 3 and the lower part should be at the inside of the electrolytic solution 3.