A plug-in connector (1) has an insulation body (3) which holds electrical contacts (4, 41 and 411), for example contact pins or contact tubes, in bores (6) which extend in the axial direction. On its outside (3a), said insulation body has a groove (8) which opens outwards and which intersects the holes or bores (6) for the contacts (4 and 411) over part of their radial extension. A retaining ring (9) fits into the groove (8) and in the working position, simultaneously engages in groove-type recesses (7) provided on the contacts (4), hereby fixing the contacts in an axial direction. The retaining ring (9) can also support at least one retaining tongue (10) protruding preferably radially inwards in the plane of the retaining ring. Said retaining tongue extends into the area of a wider bore for a middle contact (41) through a channel or opening (14) in the insulation body (3) and in the working position, engages in the recess thereof so that this contact (41), which is located outside of the ring area, is also axially fixed.