PURPOSE: To operate a dobby at a high speed without inducing troublesome vibration by making operating knives selectively cooperative with a shaking double hook going and returning motions through a pin engaging with grooves on a synchronously rotating drum.

CONSTITUTION: In a weight-closing shed dobby, rocking double hooks 13 are rotatably fitted to at each upper end of each vibrating lever 14 connected to plural heald frames through bar devices 15 and two action knives 11 selectively cooperating with the hooks 13 are provided in capable of going and returning. Two drums 16 are respectively supported with shafts 17 arranged in crossing to axes of the knives 11 in parallel and the drums 16 are constructed to be capable of synchronously rotating driven through transmitting parts of transmitting parts of the belt 18 and the pulleys 19 or transmitting parts of the chains or the gears. Further, pins 11a located at axial end of the knives 11 are engaged in curved grooves 16a engraved in the drums 16 to give desired motion of going and returning to the knives 11.