A telecommunications apparatus that has a substantially box-shaped subrack having a back wiring board mounting a connector and a plurality of shell-type plug-in units inserted in the subrack so that a connector of each of the plug-in units is connected to the connector of the subrack, further includes a flexible, electrically conductive seal member elastically deformedly disposed between a lateral surface of the plug-in unit inserted into the subrack and an interior portion of the subrack so as to enclose both the plug-in unit connector.