Abstract: A thread catcher of a cutting device in sewing machines is actuated by an air cylinder whose piston has two portions of unequal diameter. The small cylinder space accommodating the smaller-diameter piston portion is permanently pressurized while the larger cylinder space is alternately pressurized and vented. The larger cylinder space portion on its end closer to the smaller piston portion is permanently vented through a conduit. Both this conduit and the conduit for supplying the larger cylinder space include a throttle. The obtained effect is that the first step of motion of the thread catcher is quick and exact in duration, while the second step of motion is slower but performed with a greater force, so that thin threads are prevented from tearing prematurely and thick threads are cut reliably.