To provide a device and method for controlling operation of a plasma arc type melting furnace reliably grasping generation of stray current of the plasma arc type melting furnace and operating with a favorable state on the basis of the grasp.

This plasma arc type melting furnace 10 has a furnace body of which furnace inner wall made of a refractory material is coated with iron shell and generates plasma arc between electrodes inserted facing the furnace body. The furnace comprises a plasma arc detection means consisted of a first ammeter 31 for measuring current between the main electrode 11 and the furnace bottom electrode 12, an infrared camera 25 taking picture of a plasma arc generating part inside the furnace through a transmission window from outside of the furnace, and an image processor 28 analyzing plasma arc state from the images taken by the infrared camera, and a determination means 30 determining presence of stray current generated inside the melting furnace from the current measured by the current measurement means and the plasma arc state detected by the plasma arc detection means.