A weft thread cutting device for shuttleless looms is placed between a fabric edge, a comb and a warp mouth, on one side, and a weft thread selector, on the other side. Weft threads, coming from a plurality of eyelets, join at a vertex located at the fabric edge and at the beating line of the comb. The weft thread cutting device has a rotating disk with a cutting edge, configured to cut the weft threads by a motor which keeps the rotating disk in rotation, and a step control motor, which, through a rotating shaft provided with an eccentric, controls motion of a hinged lever swinging with respect to a longitudinal axis of the step control motor. The hinged lever is shaped, at one end, in the form of two arms, respectively resting on the surfaces of two elastic plates, and is connected, at the other end, to the eccentric.