A key safe-keeping device for installation, for example, in a hole in a door (2), a wall or the like, comprises a tubular unit (3) having an open or closed inner end, which is openably closed at its outer end by a cylinder lock (4). An apartment key (8), for example, can be kept in the unit, which key is removed through the tubular unit (3) after opening the cylinder lock (4) with a pass key or a master key (7). The tubular unit is concentric and is combined with an anchoring element in the form of a nut (11) having a thread (11b) for engagement with a thread (3b) on the tubular unit. The barrel (6) of the cylindrical lock (4) has a latching member (6a) which, when the cylinder lock is locked, engages in at least partially similarly located apertures (14; 15) in the unit (3) and the anchoring element (11). At least the inner of these apertures consists of a through penetrating hole. The arrangement prevents the release of the unit (3) from the anchoring element (11) through engagement with and rotation against the unit by means of a tool.