PURPOSE: To prevent breaking of a wire electrode and worsening of precision of a processed shape owing to the increase of the thickness of a work and worsening of the discharge effect of chips.

CONSTITUTION: A wire cut electric discharge device 1 comprises a wire driving device 7 to run a wire electrode 3, feed motors 9 and 11 to process and feed a work 5; a processing feed detecting circuit 15, and an ECU(Electronic Control Unit) 23. Signals from tachogenerators 31 and 33 to indicate the numbers of revolutions of the feed motors 9 and 11 are inputted to the processing feed detecting circuit 15 and an actual processing feed speed is inputted to the ECU 23 from the processing feed speed detecting circuit 15. After the processing feed speed is read by the ECU 23 the given number of times to average the feed speed, computation and decision are effected such that the value of the running speed of the wire electrode 3 is inversely decreased or increased according to the increase or the decrease of the average speed. Through control of a wire driving device 7, the running speed of the wire electrode 3 is varied to a computed value.