face 16a to thereby lock the swingable frame 13 in the cam follower disengaging position in the meantime the actuating mechanism 29 31 remains in the initial position as shown because the circumferential portion 23b of the cam 23 is positioned opposite to the follower tip 31a of the follower member 31 in the meantime the clutch member 34 on the actuating member 29 is held in the initial position as shown by the holding member 27 against the force of the spring 33 so that the first arm 34a may not be in the way of the locking member 26 moving to lock the swingable frame 13 now in reference to fig4 and 6 when the sewing machine is driven and the cam 23 is rotated in the direction indicated by the arrow mark and the cutout portion 23a of the cam 23 is positioned opposite to the follower tip 31a of the follower member 31 the actuating mechanism 29 31 is turned counterclockwise around the pivot shaft 24b due to the action of the spring 30 in the meantime the clutch member 34 moves to the left with respect to the holding member 27 and also turns counterclockwise around the pin 29b by the action of the spring 33 after all the actuating mechanism 29 31 turns counterclockwise until the abutment 29a of the actuating member 29 is pressed against.