to safety of operation also the device of this embodiment changes the diameters of the two pulleys between the follower clutches 13 and 15 to increase the reduction ratio of the over lock stitching device in comparison with the lock stitching because the moving torque of the overlock stitching device is in general lesser than that of the lock stitching device and rotates at high speed thus it is also one of the features of the invention that the driving reduction ratio of the over lock stitching device is larger than that of the lock stitching device so that the over lock stitching device may provide the optimum rotating speed further with respect to the feeding mechanism the feeding rate is not changed and the structure is fairly simplified the feeding movement is given to the teeth 38 in the structure shown in fig7 by means of the eccentric feeding cam 36 fixed on the hollow shaft 35 which is mounted on the upper shaft 35 to provide easy and exact feeding is also one of the features of this invention a second embodiment of this invention is illustrated in fig1 to 15 where the over lock stitching device is provided in a position shown in fig2 in the embodiment the stitching part 1 and 2 of the over lock stitching device is located on a recess formed on an edge of the bed 59 on the rear side of.