a self - locking step - by - step mechanism for an adjustment device of a vehicle seat has a clamping roller lock and a step - by - step device . the clamping roller lock a rotatable release wheel and a toothing . the step - by - step device has a ) a pivotably mounted actuating lever , b ) a driver pivotably mounted on the actuating lever and which has two driver regions which interact with the toothing of the release wheel , c ) a drag lever which has supporting surfaces which enter into contact with the driver , and d ) a spring . the spring has at least one projection . the drag lever has at least one indentation which is normally in engagement with the projection . the spring is fixed against rotating .