PURPOSE: To achieve the adjustment of the liq. filling height by reducing the supply of a liq. until a float reaches the surface of a floor, recording the height of the bed at that time, next increasing the supply of the liq. to bring the liq. level up to a target height and holding this height until the next measuring cycle.

CONSTITUTION: In the measuring cycle constituted of regular time intervals, the supply of the liq. is reduced until the float 1 used for measuring the filling height reaches the surface of the bed, and the actual height of the bed is recorded. Continuously, the supply of the liq. is increased to bring the liq. level up to the target height and this height is held until the next measuring cycle while adjusting the supply of the liq. Consequently, for example, the filling height of the liq. in an exchanging body column, particularly on the floor where the height of an ion exchanging body resin is fluctuated, is easily adjusted.