When a workpiece holder holding a workpiece is rocked around a lateral rocking axis by a work stage of a mounter and the workpiece is positioned so that one mounting surface of the workpiece faces a predetermined direction to be worked, a component is mounted on the one mounting surface by a mounting head of the mounter. When a posture of the workpiece in the workpiece holder is changed by a posture changing head of a posture changer and thereafter the workpiece holder in which the posture of the workpiece is changed is rocked around the lateral rocking axis by the work stage of the mounter and the workpiece is positioned so that the other mounting surface of the workpiece faces a predetermined direction to be worked, a component is mounted on the other mounting surface by the mounting head of the mounter.