When contact between a wire electrode and a workpiece is detected while, after wire electric discharge machining is ended, the wire electrode is moved (retraced) in the direction opposite to the machining direction along the machining path, the movement of the wire electrode is stopped. The wire electrode is moved in the offset direction from the contact position. When the wire electrode and the workpiece are brought into a non-contact state, the non-contact state is detected, and the movement of the wire electrode is stopped. The wire electrode is returned from the non-contact position to the machining path, and the wire electrode is retraced along the machining path in the state where the detection of contact between the wire electrode and the workpiece is neglected. Then, an amount of distortion of the workpiece is calculated from the contact position and the non-contact position.