a material is cut along straight lines and curved lines into a tapered configuration with a wire - shaped electrode according to an electric discharge type cutting method or an electrolysis type cutting method . when the straight cutting operation is shifted to the curved cutting operation , the pulse width of a pulsive voltage applied across the work piece to be cut and the wire - shaped electrode is decreased , or the pulse interval thereof is increased , or the open voltage is reduced , to decrease the electric energy applied to the work piece . accordingly , the width of a groove cut in a portion of the work piece where the radius of curvature is minimum in the curved cutting operation becomes equal to that in the straight cutting operation . an apparatus for practicing the cutting method is also disclosed .