A slider (19) to be slid by rotating a lever (20) is mounted in a first lever-side connector (L1). The slider (19) is held at an initial position where cam followers (17) provided on the first lever-side connector (L1) can be received into cam grooves (29). When the slider (19) is at the initial position, a part of the slider (19) projects out from the connector. Lever plates (20A) of the lever (20) are so configured that protecting edge portions (38) formed on parts of side edges of the lever plates (20A) are located substantially at the same position as or behind a projecting end part of the slider (19) when the slider (19) is at the initial position. Further, the protecting edge portions (38) are located closer in distance to rotary shafts (34) than an operating portion (20B).