Abstract: Actuating device for the reciprocating movement of the belts carrying the weft thread insertion grippers in shuttleless looms. Each belt is provided with a lengthwise series of slots and with the slots of one series a respective gear wheel is in mesh engagement. An oscillating gear sector drives the gear wheel. The gear sector has along a radial line thereof a slotted link coupling including a runner. The coupling provides articulation both with the big end of a connecting rod in a crank mechanism, which is driven by a cyclic shaft of the shuttleless loom, and with the pin of a rocker arm following the oscillations of the gear sector. The law of motion determined by the cooperation of the slotted link coupling and the runner causes variation of the transmitted speed, acceleration and stroke, particularly near the two dead points of oscillation of the sector thereby improving the operations of the grippers to which such motion is transmitted.