A projection (9) is provided in a male connector (1). A lever (16) is rotatably provided in a female connector (2). The lever (16) has a curved groove (18). When the lever (16) is turned, the projection (9) is inserted into the groove (18). As the projection (9) is inserted into this groove (18), the connection between the male connector (1) and the female. connector (2) is strengthened. At that time, the lever (16) provides leverage. Moreover, the distance between the fulcrum for this lever and a point of action gradually decreases. Furthermore, in this case, the groove (18) is formed in such a way as to extend to the turning center portion of the lever (16), so that the distance between the fulcrum for the lever and the point of action is reduced still more. Consequently, a larger connecting force can be provided thereto.