A receptacle connector includes a peripheral shell with a counter connector accommodating portion formed therein and opening in a fitting direction, the peripheral shell is composed of a metal portion and a resin portion, the peripheral shell has an inner peripheral surface of tetragonal tube shape with rounded corners, the inner peripheral surface being formed by one first metal flat portion, two metal curved portions and two second metal flat portions of the metal portion and one first resin flat portion, two resin curved portions and two second resin flat portions of the resin portion, and an end surface of the one first metal fiat portion situated on an opening side of the counter connector accommodating portion exposed.