An apparatus for inspection of a gap between two surfaces, at least one of which is ferromagnetic, for example in a generator, includes a sensor platform (26) for one or more sensors (26a) and an elongated mount (23), which can be moved out, for the sensor platform (26). The mount (23) can be moved in and out of the gap through an access opening, can be moved out over the length of the gap and can be rolled up outside the gap by a drive (24). In its moved-out state, the mount (23) has a curvature in a lateral cross section. In addition, the mount (23) has a plurality of magnets (27) by which the mount (23) is brought into contact with a ferromagnetic surface. The magnets (27) are attached to the side of the mount (23) facing away from the ferromagnetic surface, ensuring that the mount (23) slides along a ferromagnetic surface. The apparatus allows inspection of gaps from a height of 4 mm and is distinguished by a simple and physically small design.