A housing (10) has inserting portions (63) with projections (17) formed with slits (19). An alignment plate (60) is mounted movably on the housing (10) and has inserting portions (63) that enter the slits (19) of the projections (17). The alignment plate (60) is displaced relative to the housing (10) in the process of mounting a housing (10) on a board (90) due to interference with the board (90) and the inserting portions (63) move deeper into the slits (19). The projections (17) widen the slits (19) as the inserting portions (63) move deeper into the slits (19) and hence leading ends of the projections (17) engage opening edges of the mounting holes (92) of the board (90) to fix the housing (10) to the board (90).