A lever (4) mounted on a cover (3) is held at a standby position and, in that state, the cover (3) is fitted to a housing (1) in a connecting direction to a position where the cover (3) is not aligned with the housing (1). At this position, gear teeth of the lever (4) and rack teeth of sliders (2) do not interfere with each other and are not engaged. If the cover (3) is subsequently moved in a direction perpendicular to the connecting direction via a guiding action of the engagement of guide receiving portions (9) of the connector housing (1) and U-shaped guide portions (15) formed on the cover (3), the cover (3) is smoothly mounted at a proper mounting position. At this time, since the guide portions (15) vertically sandwich the guide receiving portions (9), upward detachment of the cover (3) is prevented.