The slow wire is a processing machine that uses a continuously moving fine wire (called a wire) as an electrode to perform a pulse spark discharge on the workpiece to remove metal and cut. Loose contact type light-pressure discharge phenomenon between the wire electrode and the workpiece during slow wire processing. When the flexible electrode wire and the workpiece are close to the discharge gap (for example, 8 to 10 μm) which is generally considered, spark discharge does not occur, and even when the wire has contacted the workpiece, the gap is often not seen when the gap is not visible from the microscope. To the spark, a normal spark discharge occurs only when the workpiece bends the tip of the wire and is offset by a certain distance (a few microns to tens of microns). At this time, each time the wire electrode feeds 1 μm, the discharge gap does not decrease by 1 μm, but the wire wire increases the tension between the wires, and the workpiece increases the lateral pressure. Obviously, only a certain slight contact pressure is maintained between the wire and the workpiece. In order to form a spark discharge. According to this, there is some kind of electrochemically generated insulating film medium between the wire and the workpiece.