To prevent an object to be worked and other structures from being damaged by preventing melted metals from being splashed, and to facilitate the collection of the melted metals.

In this working device, the object 22 is set in an atmospheric gas other than oxygen or in a vacuum, and one other hand, a plasma torch 10 opposing to the object 22 is provided In the plasma torch 10, working gas is spouted out from a torch nozzle 13, and assist gas is spouted out from a nozzle cap 18. For the working gas and the assist gas, a gas other than oxygen, for instance, N2 gas, mixed gas of Ar and Hz, inert gas is used. In the atmospheric gas or the vacuum, the object 22 is cut with a plasma arc by using a plasma stream with high temperature and high flow rate from the plasma torch 10, generated melted metals 23 are allowed to flow down, and are attached to the cut rear side of the object 22.