a horizontal portion connected to the arm 1 by a screw means 48 and a upward portion with adjustable screw means 49 movement of the shaft 50 is restricted by the screw means 49 fig2 and 9 in operation when the knob 27 is pushed in the frontward direction or is moved from a solid line position to a phantom line position in fig8 the lever 26 is rotated about the pin 28 in the counter clockwise direction with the result that the lever 26 is disengaged from the notch 21a 34 due to the counterclockwise or frontward movement of the lever 26 the rod 29 is brought into movement against the spring 31 in the frontward direction and then the swing member 34 is rotated in the counterclockwise direction against the spring 36 fig6 upon the counterclockwise rotation of the swing member 34 the projection 40a of the swing member 40 is brought into engagement with the end portion of the slot 34b and is rotated in the clockwise direction the swing member 40 and the lever 38 are so connected on the common shaft 37 that the lever 38 is then moved in the clockwise direction fig1 particularly as to the lever 38 due to the clockwise rotation thereof the horizontal portion 38a of the lever 38 is lowered and is brought into engagement with the needle bars 12 39 and 12 34 upon further downward movement of the horizontal portion 38a of the lever 38 the height of the needle bars 12 39 and 12 34 is lowered against the pawl portions 18a 39.