PURPOSE: To prevent the block of a nozzle caused by drop of a residual part and cut of a wire electrode by adding a relative movement to a corner part so that the movement may cause its biting in a work to be processed and removing the residual part produced on the corner part, in the case of a coreless machining.

CONSTITUTION: Wire cut electric discharge machining is carried out while inserting a wire electrode into a machining start hole and relatively moving a work 1 to be machined and the wire electrode toward a relative position C following a coreless path and the wire electrode is relatively moved on pathes C-D toward a relative position D so that the wire electrode may be relatively moved in a direction by which the wire electrode bites into the work 1 to be machined at a corner part like the relative position C formed by mutually connected two coreless pathes. Then, a machining is carried out in order of relative positions C, E, F, E, G starting from the relative position D and a core is entirely removed by an electric discharge machining while expanding the machining upto a nest 108 consisting of final path group following the coreless path.