Hermetically sealing device and hermetically sealing method

A hermetically sealing device attached to a bored opening bored through a side of a fluid pipe, the hermetically sealing device comprising:

• a sealing main-body;
• and
• a rubber seal adhered to the sealing main-body, wherein
• the rubber seal includes:
• an inner lip that extends along a periphery of the bored opening, and includes an outer-circumference surface that extends forward and inclines toward an inner-circumference side;
• a slit that is formed on an outer-circumference side relative to the inner lip and where an outer-surface-side edge of the bored opening enters;
• and
• an outer lip that is formed on an outer-circumference side relative to the slit that is formed on an outer-circumference side relative to the inner lip, and transforms in such a manner that the outer lip extends toward an outer-circumference side to be hermetically in contact with an outer surface of the periphery of the bored opening.