The invention relates to an adjusting device (5) for automatically actuating the vehicle door (3) of a motor vehicle, said device (5) having:—a first tubular housing (15) connected to the body (9) of the vehicle (1) and a second tubular housing (25) connected to the vehicle door (3) to be adjusted, the second tubular housing (25) can be moved telescopically relative to the first housing (15), and—a spindle drive (21) comprising: •a spindle (27), which can be rotated by an electric-motor drive arranged in the first tubular housing (15), • a spindle nut (31) threaded with the spindle (27), which when the spindle (27) is rotated, is displaced along the longitudinal axis (A) of the spindle (27), from a retracted rest position into an extended position, • a push rod (33) bearing the spindle nut (31), which extends in the direction of the longitudinal axis (A) of the spindle (27), said push rod (33) being coupled to the second tubular housing (25), • and a tubular guide part (39) enclosing the push rod (33) and the spindle nut (31) for guiding the spindle nut (31) during its axial displacement According to the invention, said guide part (39) is provided with a shape complementary to the shape of the spindle nut (31), to secure the spindle nut (31) against rotation relative to said guide part (39), and in that said guide part (39) is produced by a plastic forming process on a suitable metal tube.