of the abutment 18 of the phase detecting arm 13 in dependence upon the engagement of the follower 12 with the cam faces a b and c sw 2 is a final stitch detecting switch and the actuator 19 is moved to operate the switch sw 2 by a turning movement of the abutment 18 in dependence upon the engagement of the pin 14 with the grooves 7 the numeral 20 is a releasing arm carrying a follower pin 21 and is turnably mounted on the shaft 16 the pin 21 cooperates with the releasing cam 9 to turn the arm 13 in the clockwise direction thereby disengaging the pin 14 from the groove 7 each time when the arm 13 is axially moved in the leftward direction so that the stitching type may be changed the numeral 22 is a pulley which is as shown mounted on one end of the upper shaft 2 and receives the driving force of a machine motor not shown via belt 23 the numeral 24 denotes a stopping cam secured to the upper shaft 2 to stop the upper shaft 2 when the abutment 25 of the cam 24 engages the end 27 of a pawl 26 which is turnably mounted on a pivot 28 secured.