A connector including a first connector element and a second connector element that are coupled into a single unit, in which the first connector element has an engagement projection that projects interior of the first connector element and extends in the direction of the depth of the first connector element so that the front end of the engagement projection is spacedly apart from the front edge of the first connector element, and the second connector element is formed with an engagement slit that extends in the direction of depth of the second connector element and engages with the engagement projection of the first connector element.