PURPOSE: To get rid of changes in the processing gap width according to processing direction in such a way that wire is vibrated without contacting, and its vibrating direction is controlled.

CONSTITUTION: When high frequency pulse from power source 15 for processing is applied between a work piece 1 and wire 9, spark discharge is produced between the lateral bulkhead of a slit 1a which has been made by being shaven off by electric discharge, the slit 1a is running on to be extended. In the meantime, a table 2 is driven by an X driving circuit 3 and a Y driving circuit 4, the cutting direction of the slit is made the way to a settled direction. Further, the wire 9 vibrates by existence of a permanent magnet 10 having N pole 10a and S pole 10b. Vibrating direction of this vibration is controlled to meet the moving direction of the slit 1a with use of a servo motor 8.