The present invention relates to an electric discharge machining device which supplies a current pulse to a machining gap (9) while switching polarity. The electric discharge machining device includes: a first switch (41) provided between the positive pole of a power supply (30) and a work piece (4); a second switch (42) provided between the negative pole of the power supply and the work piece; a third switch (43) provided between the negative pole of the power supply and a tool electrode (2); a fourth switch (44) provided between the positive pole of the power supply and the tool electrode; and a pulse generating device (10). In order to supply a series of current pulses to the machining gap with a straight polarity, the pulse generating device repeatedly switches on and off either the first or third switch while the other switch is on. In order to supply a series of current pulses to the machining gap with a reverse polarity, the pulse generating device repeatedly switches on and off either the second or fourth switch while the other switch is on.