PURPOSE: To securely prevent any liquid leakage of electrolyte by adjusting the difference between the outer diameter of the O-ring touching part of a terminal pole and the inner diameter of an unworked O-ring larger than the difference between the outer diameter of the unworked O-ring and the inner diameter of the O-ring touching part of the terminal-pole penetrating hole.

CONSTITUTION: An O-ring 7 is attached between a terminal pole 6 and an O- ring touching part 3 of a terminal-pole penetrating hole 2. The symbol 8 represents a teminal which is joined to the terminal pole 6. The O-ring 7 is pressed and held between the terminal 8, and a step-like part 4 of the hole 2. The symbol 9 represents a sealing agent in which the terminal 8 is buried. The dfference between the outer diameter of the O-ring touching part 3 of the terminal pole 6 and the inner diameter of the unworked O-ring 7 is adjusted to 15∼30% of the central diameter of the unworked O-ring 7. The difference between the outer diameter of the unworked O-ring 7 and the O-ring touching part 3 of the terminal-pole penetrating hole 2 is adjusted to 5∼10% of the central diameter of the unworked O-ring 7.