To surely detect the fall of a work from a suction tool when carrying the work with the suction tool.

When the pressure Pin in an attaching/detaching passage becomes the suction detecting pressure Pj or less, the suction of the work is detected, and carrying operation is started. During carrying, as long as the pressure Pin in the attaching/detaching passage does not exceeds an upper limit value of a fall detection range, the work is determined it has not been dropped from the suction tool. The fall detection range is computed by adding the predetermined allowable fluctuation width ΔD to the pressure Pin in the attaching/detaching passage read as the reference pressure with the work sucked by the suction tool.