A receptacle connector 20 includes a housing 200 in which a recess 203 for housing a plug connector 30 is formed on a side opposite to a surface mounted on a substrate of the housing, a required number of contacts 220 arranged between end portions of the housing 200, and reinforcement metal fittings 230 each of which is provided on one of the end portions of the housing 200. The reinforcement metal fitting 230 has a cantilever resilient piece 235 that extends in the arrangement direction of the contacts 220, and a contact piece 236 that extends from a free end portion of the cantilever resilient piece 235 and comes into contact with the plug connector 30 when the receptacle connector 20 and the plug connector 30 are fitted to each other.