engagement means just like that in a later described second manually operable knob which brings about a prevention of further rotative movement of the actuating arm 16 because of the contacting of the engagement pin 18 against lug 15a of regulating plate 15 when first knob 13 is operatively rotated therefore regulating plate 15 and actuating arm 16 are jointly rotated to change as above mentioned the distance between roller 132 carried by needle bar oscillating rod 130 and the oscillating fulcrum of oscillating arm 133 by which the amplitude of oscillation imparted to the needle bar 131 is to be changed in this way an amplitude regulator is composed of oscillating arm 133 roller 132 link 17 actuating arm 16 etc on a shaft 24 which is rotatably carried by auxiliary plate 12 are secured a second manually operable knob 23 hereinafter simply referred to as second knob 23 in this description and a feed regulating cam body 25 for being jointly rotated therewith on the edge of cam body 25 is formed a cam surface 25a for setting a length of forward feed movement a leaf spring 26 is secured with a screw 27 on the back of auxiliary plate 12 on the tip of leaf spring 26 thereof is fixed an engagement pin.