Abstract The quality of the surface machined by electrical discharge machining (EDM) depends on the degree of discharge dispersion. In this paper a dot-matrix EDM with scanning motion is proposed in order to realize rapid prototyping by EDM and to control the discharge position in real machining. The machining process by the dot-matrix method is similar to the printing motion with a dot impact printer. The developed machining unit has six electrode feeding devices each of which controls the position of a thin wire electrode independently by inchworm mechanism with piezoelectric actuators. Discharge current is supplied to each wire electrode also independently in order to realize complete discharge dispersion. 3 dimensional shape with crack-less surface is machined by scanning motion of the unit.