4 the variation being caused by the movement of the movable guide roller 5 this enlarges an area of the power supply element 4 that is abraded due to contact with the wire electrode 10 resulting in prolongation of the life of the power supply element 4 fig4 is a schematic view of a lower guide block 1 of a third embodiment in which a guide roller s driven by a small motor 6 through a lead screw 7 is located below a power supply element 4 in this embodiment the variation range of the contact position of a wire electrode 10 on the power supply element 4 is widened by disposing the power supply element 4 and the guide roller 5 located below the power supply element 4 close to each other thus the life of the power supply element 4 is extended as illustrated in fig5 a 5 d the movable guide rollers 5 5 a and 5 b in each embodiment have respective portions that guide the wire electrode 10 that are formed into the shape of v as shown in fig5 a the shape of a curved concave as shown in fig5 b the shape of a saucer shaped concave as shown in fig5 c the shape of a concave with both sides standing upright as shown in fig5 d or the like the shapes of the guide rollers would be adequate as long as they enable the wire electrode 10 to move in a direction perpendicular to the running direction thereof and are able to guide the running of the wire electrode.