A pneumatically operable adjusting device (1) is provided for acting on a spring device (5) of a spring damper device (3) having a tubular body (2), with a tubular piece-shaped housing (4) which is designed to surround the tubular body (2) and has a passage (6) passing through a peripheral wall of the housing (4), and the adjusting device (1) has an adjusting nut (9) with an internal thread (10) which is attached to an external thread (11) of a tubular body (2), 37) of the spring damper device (3) can be brought into screw engagement, the housing (4) being designed for releasable abutment against the adjusting nut (9) and having an inner recess (7) for forming a pressure chamber (8) which is in fluid connection with the passage (6) and the inner recess (7) forming a pressure wall (24), the fluid admission of which causes a force acting on the housing (4) in the axial longitudinal direction and the housing (4) has an abutment surface (54) designed for spring force admission by the spring device.