PURPOSE: To make it possible to begin the insertion work of a wire electrode from a transfer trajectory of high probability, by renewing and storing transfer trajectories at the time when contact is released in respective relative transfer processes, at every relative transfer operation, and reading and carrying out the stored transfer trajectory at the staring time of a relative transfer operation.

CONSTITUTION: A workpiece 2 to be processed and a wire electrode 1 in contact with each other are relatively transferred on a specified transfer trajectory until the contact is released, and when the contact is released, the relative transfer is stopped. And, when the wire electrode 1 is inserted into process bigining holes 2a, 2b, 2x provided on the workpiece 2, transfer trajectories at the time when the contact is released in relative transfer process are renewedly stored in a memory means 13 at every relative transfer operation, and when a relative transfer operation is started, the last trajectory stored in the memory 13 is read out and carried out with a reading means 14. Thereby the insertion operation of the wire electrode 1 can be started from a transfer trajectory of high probability.