A fastening device for actuating cylinders with longitudinal stringers (2, 3) extending axially along a cylinder tube (1). A fastening yoke, e.g. comprising two halves (6a, 6b), is clampable with the aid of at least one clamping screw (8r) for fixing it in a desired axial position along the cylinder tube. In accordance with the invention the opposing clamping portions (6ar, 6br) of the fastening yoke act on two intermediate clamping blocks (10ar, 10b) which are thus pivoted in opposite directions, so that clamping is achieved exclusively against the inner and outer side portions (2i, 2y and 3i, 3y), whereby internal deformation of the cylinder tube (1) is prevented.