The fixing device which serves for retaining a rail (1), in particular a running or guide rail, has a strip (2) which is provided with an angular profile and can be connected with little outlay on one side to a wall (9) and on the other side to a rail (1). The strip (2) has two limbs (21; 22) which are provided for holding the rail (1), the first limb (21) of which is provided with openings (23) for the passing through of fixing screws (24) which can be connected to the wall (9), and the second limb (22) of which is provided with a T-profile-shaped longitudinal slot (25) which is open towards the rail (1) and serves for holding and for retaining a locking element (3) which preferably has a thread (31) for a mounting screw (32) which can be connected to the rail (1), or is connected fixedly to said mounting screw.