Each of contact portion rows 310 and 320 includes an outer contact portion 212 and an inner contact portion 216 forming a differential pair. In a Y-direction, the outer contact portion 212 and the inner contact portion 216 of the contact portion row 310 are located at same positions as those of the other contact portion row 320, respectively. A main portion 430 of a mid-plate 400 is located between the contact portion rows 310 and 320 in a Z-direction. Between the main portion 430 and each lock portion 450, a space 500 is provided to allow resilient deformation of a spring portion 460. A side edge 432 of the main portion 430 that oriented outward in the Y-direction is located between an inner edge 212A of the outer contact portion 212 and the lock portion 450 in the Y-direction.