An electric discharge machine for machining a workpiece (2a) made of insulating material or other materials comprises: a first comparison member (17) for comparing voltage (V) between the electrodes of the electrode (1) and the workpiece (2a) with the first reference voltage (V1) which is set at a value close to electric power source voltage (V0) not higher than electric power source voltage (V0); a second comparison member (18) for comparing voltage (V) between the electrodes with the second reference voltage (V2) which is set at a value lower than the first reference voltage (V1); and a control member (19) for setting a short electric discharge pulse width (TP1) in the case where voltage (V) between the electrodes is lower than the second reference voltage (V2) according to the result of comparison conducted by the second comparison member (18) at a point of time when a predetermined period of time (T0) has passed from the time when voltage (V) between the electrodes becomes lower than the first reference voltage (V1) according to the result of comparison conducted by the first comparison member (17), and for setting a long electric discharge pulse width (TP2) in the case where the voltage between the electrodes is higher than the second reference voltage (V2). This electric discharge machine is capable of stabilizing the machining of the workpiece (2a) made of insulating material or other materials and also capable of enhancing quality of a machined face.