The object of the present invention is to make it possible to maintain a stable electric discharge and to achieve a stable quality and machining performance even when a work having a non-uniform composition is machined. A wire electric discharge machining device performs electric discharge machining on a work while controlling an inter-electrode distance between a wire and the work based on an inter-electrode voltage between the wire and the work so as to match a set target voltage. The wire electric discharge machining device includes an inter-electrode voltage measuring unit that measures the inter-electrode voltage, an actual amplitude calculating unit that calculates an amplitude of the measured inter-electrode voltage, and a target voltage correcting unit that corrects the target voltage in such a way that the calculated amplitude approaches the target amplitude that is set to a value larger than zero.