PURPOSE: To enable to measure accurate residual amount without being effected with the shape of vessel, by sectioning the liquid containing vessel into equal parts and reversing the reversible pump when one chamber is vacant or when another chamber is full.

CONSTITUTION: The vessel 1 containing the liquid 3 is sectioned into the first chamber 15 and the second chamber 16 having equal volume with the section plate 14, liquid is moved from one to another with the reversible pump 19, and the reversible pump 19 is reversed when the liquid in this chamber is vacant or that in another chamber is full, to move the liquid to opposite room. After that, this operation is repeated, the residual amount of liquid in the vessel is measured by measuring the delivery amount of the period until the next reversing from the reversing of the reversible pump.