A key safekeeping device for fitting into a hole in a door, wall or corresponding structure includes a first tubular element (10) that carries a first collar (12) on an outer end thereof. A lock cylinder (14) is detachably fitted to the first tubular element. A second tubular element (20) that carries a second collar (22) is intended for lockable engagement with the first tubular element. At least one of the collars is comprised of a separate ring-shaped part (22) that includes an internal aperture for receiving a blocking means (24) in the form of a bent/curved element that is intended to be fitted into a peripheral groove (20c) in the barrel surface of the second tubular element. The blocking element, which lies hidden in the aperture of the ring-shaped part, cannot therefore be removed when the key safekeeping device is fitted and the lock cylinder is mounted in place. Because the collars can be produced as separate parts, the key safekeeping device can be manufactured from tubing of any appropriate material thickness, therewith minimizing the cutting work required in manufacture. This provides gains with respect to tool costs, material consumption, working time and therewith also in respect of the environment.