A receptacle connector includes a receptacle ferrule, a receptacle housing and a spacer. The receptacle ferrule has a first front end portion having a receptacle interface part In the receptacle housing, the receptacle ferrule and a plug connector having a second front end portion having a plug interface part configured to be optically coupled with the receptacle interface part are to be accommodated. The spacer has a first surface configured to contact the first front end portion, and a second surface configured to contact the second front end portion. The spacer is arranged in the receptacle housing. At a state where the first front end portion is contacted to the first surface of the spacer and the second front end portion is contacted to the second surface of the spacer, the receptacle interface part and the plug interface part face each other at a predetermined interval.
