Abstract: There is disclosed a buttonhole bar tacker sewing machine with a device for controlling the length of the buttonhole terminated by a wedge bar tack, the machine having a support plate for the workpiece and control members for exerting a reverse motion in the direction of the longitudinal axis of the buttonhole. The control device comprises a first cam, a cam for forming a wedge bar tack and at least one further cam coupled in its motion with the first cam for bar tacking the eye of the buttonhole. The further cam for bar tacking the wedge bar tack of the buttonhole is arranged reversibly rotatable about its axis of rotation and adjustable in its angular position and adjustable relative to the first cam and is further reversibly coupled in its motion with the reversible motion of the support plate in the direction of the longitudinal axis of the buttonhole.