An apparatus for propulsion inside an oblong cavity, such as pipes or the like, is disclosed. The apparatus is characterized by comprising a central rotating part comprising an inclined wheel construction arranged to thrust towards the inner wall of the cavity, in that the central rotating part comprises a plurality of roller elements (1) arranged in a row against each other, and two adjacent roller elements (1) in the row comprise mutually adjacent inclined sliding faces (15), so that each element is arranged to be displaced in radial direction outward from a central shaft (11) due to axial compression of the unit of inclined roller elements, until the corresponding wheel construction abuts the inner wall of the cavity, and that the wheel construction includes that a bearing construction is arranged enclosing around each roller element, and being rotatably independent of its corresponding roller element, and is mounted at an inclined angle defining the climbing angle of the apparatus during propulsion, and further the apparatus comprises drive means for rotation of the rotatable part. It is an essential feature of the apparatus that it comprises internal rotational counter force, and that automatic transmission may be provided.