A variable member is connected to a rod-shaped member and connected to a tube portion to ensure airtightness within a housing, and deforms when the rod-shaped member is displaced relative to the housing along an axial direction. A position of the connection between the tube portion and the variable member in the axial direction is a position shifted from a rear end of a gap toward a front side by a predetermined length or a position at the front side with respect to the position shifted by the predetermined length. The predetermined length is a length which is 50% of a length of the gap in the axial direction.