Wire electric discharge machining apparatus

A wire electric discharge machining apparatus having a structure for supplying power to a wire electrode, the structure being capable of prolonging the life of a power supply element and reducing a manufacturing cost and a running cost with a simple structure. There is provided a guide roller for guiding the wire electrode above and/or below the power supply element formed into a flat plate. The guide roller is driven by a small motor through a lead screw. An oscillating direction is perpendicular to a running direction of the wire electrode and parallel to a flat surface of the power supply element. A contact position of the wire electrode on the power supply element is varied in an area of a wide range, so that the contact position is not focused, thereby creating no groove or the like, that is attributable to friction, in the power supply element and extending the life thereof. The power supply element is formed into a simple flat plate, reducing the manufacturing cost thereof. The guide roller and the driving mechanism thereof also have simple structures, thus reducing the manufacturing and the running cost.