A plug-in connector has an insulating body which holds electrical contacts, for example contact pins or contact tubes, in bores which extend in the axial direction. On its outside, the insulating body has a groove which opens outwardly and which intersects the holes or bores for the contacts over part of their radial extension. A retaining ring fits into the groove and in the working position, simultaneously engages in groove-like recesses provided on the contacts, thereby fixing the contacts in an axial direction. The retaining ring can also support at least one retaining tongue protruding preferably radially inwardly in the plane of the retaining ring. The retaining tongue extends into the area of a further bore for a middle contact through a channel or opening in the insulating body and in the working position, engages in the recess thereof so that this middle contact is also axially fixed.