A recess (67) is formed in a connection surface of a housing. A nut (52) is inserted into the recess (67) and fixed to the housing in a state exposed on the connection surface. A sealing material is introduced into the recess (67), and the outer peripheral surface of the nut (52) is coated with the sealing material. The recess (67) of the housing includes a first surface (71) arranged to face the outer peripheral surface of the nut (52) while forming an introduction space (74) for the sealing material between itself and the outer peripheral surface of the nut (52), a second surface (72) arranged to project radially outwardly from the opening edge of the first surface (71) and a third surface (73) arranged from the outer end of the second surface (72) to the connection surface in a direction crossing a projecting direction of the second surface (72).