Two supports (24) are formed on one side surface of a first housing (20) at positions symmetrical to a center of a connection area with a second housing (40) in a lengthwise direction (L). The lever (60) is selectively mounted in a first mode on one of the two supports (24) and rotated toward one side or in a second mode on the other support (24) and rotated toward the other side. The lever (60) has a first and second parts for exerting pushing forces on the first housing (20) in a direction to proceed with a connecting operation of the housings (20, 40) as the lever (60) is rotated. The first part is a cam groove (68) engageable with a follower pin (43) of the second housing (40) and the second part is a recessed groove (73) engageable with the support (24) not supporting the lever (60).