A mechanism for connecting first and second members through a sealing member sandwiched therebetween includes a position adjustment portion which adjusts a position of the first member in a direction substantially perpendicular to a surface of the second member with respect to the sealing member arranged on the second member, a reference portion which is provided to the second member and has a reference surface substantially perpendicular to the surface of the second member, and a pressing portion which presses the first member in a direction substantially parallel to the surface of the second member against the reference surface of the reference portion. A positioning member is provided to the first member and comes into contact with the reference surface of the reference portion, with the positioning member being position-adjustable with respect to a reference position of the first member. The first member, while being separated from the sealing member by the position adjustment portion, is positioned by the reference portion and pressing portion in the direction substantially parallel to the surface of the second member, and is thereafter moved by the position adjustment portion in the direction substantially perpendicular to the surface of the second member to deform the sealing member.