The invention relates to a pneumatic adjustment device (4) for adjusting a side part (3a) of a vehicle seat from a base position into an actuation position, the adjusting device (4) has a double-armed lever (7) with an outer lever arm (7b) and an inner lever arm (7a) for adjusting the sides (3a), an inflatable blowing device for adjusting the inner lever arm (7a), such as a bubble (10), and a mechanical spring device (9) for adjusting the inner lever arm (7a). According to the invention, the blowing device (10) is filled in a basic position of the adjusting device (4), the spring device (9) is tensioned in the basic position and pretensions the inner lever arm (7a) into the actuation position, and the spring device (9) presses the air bubble (10) in the actuation position, a locking device (12), for example a locking air bubble (18), is provided, the locking device can be adjusted between an unlocking position and a locking position and locks the basic position in the locking position for unloading the blowing device (10).