PURPOSE: To facilitate the assembling work of a pair of electrodes and to decrease the number of fixing parts of electrode plate and spacers by tightening members, by forming a plurality of spacers, which are provided between the electrode plates in strip shaped sheets, which are extended in the direction of the liquid level displacement of the electrode plates.

CONSTITUTION: A pair of electrode plates 1 are constituted by two flat plane electrode plates 3 and 3a and spacers which hold the size between the electrode plates constant. The spacer 12 is formed in a strip shaped sheet, which is vertically extended in the direction of the liquid displacement of fuel shown by an arrow A. In each electrode plate a plurality of tightening member inserting holes 31 and 3a1 are provided at parts where the spacers 12 are arranged. The neighboring spacers 12 are linked by couplings 14, which are thinner than the spacer 12. A thin easily breakable part 15 is formed at each linking point of the spacer 12 and the coupling 14.