To provide a method for fitting a thin cord element like a harness cord of a jacquard type weaving system, capable of accurately and effectively controlling the thin cord element.

In this method for assembling a thin cord 3 in an opening forming apparatus in a jacquard type weaving machine, at least one end 3a of the thin cord element 3 which is wound at least once and driven by rotors 6 and 7 of an electric rotary actuator is fixed to a pulley 2, and a means for detachably connecting the thin cord element 3 to the actuator 1 is installed.