PURPOSE: To save the cost and prevent a defect in operation as to the automatic level adjusting device which automatically adjusts the level of the stored liquid in the tank within a certain range.

CONSTITUTION: On an installation surface, the tank T is supported so that the lower part of the tank T swings via a swing support shaft 4 between a 1st tilt position where the tank slants to one side and a 2nd tilt position where the tank tilts to the other side. An air chamber A of specific capacity is provided in the tank so that moment swinging the tank from the 1st tilt position to the 2nd tilt position when the liquid level in the tank rises to an upper-limit level Lmax or moment in the opposite direction from the moment when the liquid level falls below a lower-limit level operates on the tank; and the relative positions of the air chamber A and swing support shaft 4 are set and a liquid replenishment duct 1 for replenishing liquid into the tank is provided with a shut-off valve V which is associated with the swing of the tank T.