A lever 22 is pivotally supported on a male connector 21 through bosses 27, and an engagement projection 30 is formed on a lower portion of a front end portion of each side wall 28 of the lever 22, and a side projection 31, which is disposed beneath the boss 27 in an initial fitting condition, is formed on each side wall 28. Guide step grooves 37 for respectively guiding the side projections 31 are formed in an inner face 32A of a hood portion 32 of the female connector 23. A first step portion 37A and a second step portion 37B are formed intermediate opposite ends of the guide step groove 37. When the side projection 31 abut respectively against the side projections 31, the engagement projections can be engaged respectively in engagement grooves 35. Therefore, the lever 22 is provisionally retained by the second step portions 37B, and in this condition the lever 22 is pivotally moved so as to positively engage the engagement projections 30 respectively in the engagement grooves 35. Therefore, the lever 22 will not idle, and the male connector 21 can be positively fitted into the hood portion 32.