A method of operating a wire electric discharge machine comprising an auxiliary discharge circuit (7, 9) for applying a voltage to an inter-electrode gap between an electrode and a workpiece and a main discharge circuit (8, 10) for supplying a machining current to the inter-electrode gap, the method comprising: applying, by the auxiliary discharge circuit (7, 9), a voltage to the inter-electrode gap, for inducing electric discharge; machining the workpiece by repeating a cycle in which the main discharge circuit (8, 10) is activated and stopped after the auxiliary discharge circuit (7, 9) is activated; and measuring, by a discharge delay time measuring unit, a discharge delay time, which is a duration without electric discharge resulting in the voltage being applied from the auxiliary discharge circuit to the inter-electrode gap, and measuring a duration in which an absolute value of an inter-electrode machining voltage waveform is not lower than a threshold, wherein, if no electric discharge is generated after the lapse of a predetermined short-circuit detection period, since the application of the voltage from the auxiliary discharge circuit (7, 9) and the absolute value of the inter-electrode machining voltage is lower than the threshold, the inter-electrode gap is deemed to be short-circuited and the discharge delay time is set to zero; wherein a short-circuit machining current is supplied from the main discharge circuit to the inter-electrode gap if, after the lapse of the predetermined short-circuit determination period since the start of the application of the voltage by the auxiliary discharge circuit (7, 9), the result of measurement by the discharge delay time measuring unit is zero, no machining current or a machining current lower than the short-circuit machining current is supplied from the main discharge circuit (8, 10) if an electric discharge is generated and if the discharge delay time is less than a reference value, the reference value being longer than the predetermined short-circuit detection period, and a normal machining current higher than the short-circuit machining current is supplied from the main discharge circuit (8, 10) when the absolute value of the inter-electrode machining voltage waveform is not lower than the threshold, electric discharge is generated and if the discharge delay time is not less than the reference value. applying, by the auxiliary discharge circuit (7, 9), a voltage to the inter-electrode gap, for inducing electric discharge; machining the workpiece by repeating a cycle in which the main discharge circuit (8, 10) is activated and stopped after the auxiliary discharge circuit (7, 9) is activated; and measuring, by a discharge delay time measuring unit, a discharge delay time, which is a duration without electric discharge resulting in the voltage being applied from the auxiliary discharge circuit to the inter-electrode gap, and measuring a duration in which an absolute value of an inter-electrode machining voltage waveform is not lower than a threshold, wherein, if no electric discharge is generated after the lapse of a predetermined short-circuit detection period, since the application of the voltage from the auxiliary discharge circuit (7, 9) and the absolute value of the inter-electrode machining voltage is lower than the threshold, the inter-electrode gap is deemed to be short-circuited and the discharge delay time is set to zero; wherein a short-circuit machining current is supplied from the main discharge circuit to the inter-electrode gap if, after the lapse of the predetermined short-circuit determination period since the start of the application of the voltage by the auxiliary discharge circuit (7, 9), the result of measurement by the discharge delay time measuring unit is zero, no machining current or a machining current lower than the short-circuit machining current is supplied from the main discharge circuit (8, 10) if an electric discharge is generated and if the discharge delay time is less than a reference value, the reference value being longer than the predetermined short-circuit detection period, and a normal machining current higher than the short-circuit machining current is supplied from the main discharge circuit (8, 10) when the absolute value of the inter-electrode machining voltage waveform is not lower than the threshold, electric discharge is generated and if the discharge delay time is not less than the reference value.