PURPOSE: To improve the accuracy in measuring the remaining volume of liquid by forming dividedly at least the one electrode plate of the electrode plates which are spaced from each other and are disposed opposite to each other in a vessel in the curved part thereof and connecting the divided plates by means of a conductive member.

CONSTITUTION: A baffle plate 4 serving as the 1st electrode plate is bent to the lateral direction by the curved part 7 along the vertical direction. The 2nd electrode plate 6 which is spaced from the inside surface on the curved side of the plate 4 and is disposed opposite thereto is dividedly formed in a lateral direction of two sheets of electrode pieces 6', 6". The two pieces 6', 6" are connected by means of a curved connecting member 12 provided in one body thereto. Since the pieces 6', 6" are formed of flat plate-like members together with the plate 4, the electrode pieces parallel to the plate 4 when mounted to the plate 4 with a spacer 5 having an insulation characteristic, whereby a specified space is assured.