A first housing 10 is arranged in a mounting hole 91 of a panel 90. The first housing 10 includes a base portion 27, a coupling portion 28 located forward of the base portion 27, a linking portion 29 linking between the base portion 27 and the coupling portion 28, and a lock arm 30 projecting rearward toward the base portion 27 from the coupling portion 28. The lock arm 30 has a lock surface 34 to be arranged to contact a front surface of the panel 90. The lock arm 30 and the linking portion 29 are both shaped to be resiliently deformable.