PURPOSE: To construct a heavy dobby to correctly operate even in the case of linking with a loom driven at a high speed.

CONSTITUTION: This heavy dobby has a closed shed and has two actuation knives 17 movable by reversed displacements for selectively co-operating with a rocking double hook 14 supported by rocking levers 11 connected to a heald frame of a corresponding loom under an action of a pusher of a reading mechanism of the dobby. Further, the heavy dobby is composed of two functional locking members releasing a knife 17 at an instant of one side controlling or selection, that is, an instant that two knives 17 are simultaneously brought into contact with the rocking lever 11 and co-operating with an elastic returning device. Each rocking lever 11 is made to transversely acting each of the rocking lever 11 to corresponding rocking double hook 14 for angularly locking the double hook in the case of clamped by the actuation knife 17.