A first connector 30 comprises a connector body 31, and an engaging lever 32 pivotally supported by a pivot 33 such that one end of the engaging lever project from one end surface of the connector body 31. An engaging projection 43 project from one end of the engaging lever 32, and a connecting projection 40D projects from the other end of the engaging lever 32. A second connector 50 is formed at its inner wall with a guide groove 54 for guiding the connecting projection 40D. By fitting the second connector 50 to the first connector 30 in a temporarily mounting state in which the engaging projection 43 engages the mounting member 20, the connecting projection 40D is guided in the guide groove 54 to turn the engaging lever 32, and the engaging projection 43 is supported by the mounting member 20.