Levelling device

The instrument has a housing (1) fastened to a vertical surface e.g. tile (4) or room wall (5), by a fastener. A light beam device associated with the housing irradiates a light beam (7) emerging on the vertical surface as a line. A level indicator (8) brings the housing into a defined rotational position relative to a horizon. The level indicator is rotatably associated with a level carrier (9) assigned to the housing. The housing is fastenable with a reversible adhesive agent in any rotational position and lateral position at a retaining plate (2) forming the fastener. The retaining plate is made from a ferromagnetic material. The light beam device is a semiconductor laser. The adhesive agent is a hook and loop fastener.