Abstract: A thread cutting device applicable to sewing machines includes elements connected to a support plate to be installed in the sewing machine at the position therein where the common sliding elements are to be located. The support plate has a screw which acts on a bridge element when the bridge element is pressed against the lower face of a panel of the machine. One of the elements of the thread cutting device has a generally Y-shaped configuration and is provided with an alternating lineal movement, either by means of manual, electro-pneumatic or electromagnetic operation, in directions parallel to that of the sewing of the machine. Such shaped element angularly operates a movable knife against a fixed knife in synchronized cooperation with a thread collecting hook which also has an angular displacement. The arrangement further includes a thread withdrawing device and a thread tension opening device.