1. A method of determining electric discharge machining conditions in a machining gap formed between an electrode and a workpiece based on a set of predefined machining parameters including machining area, electrode undersize, machining depth, electrode material and workpiece material, the method comprising the steps of: establishing multiple sets of predefined machining parameters; establishing, for each set of predefined machining parameters, a set of basic machining data indicative of relationships among electric discharge machining current, machining depth and minimum electrode side surface undersize during electric discharge machining; selecting at least two sets of basic machining data from among the multiple sets thereof in accordance with a given set of predefined machining parameters; and inferring and generating machining condition data representing a series of pairs of machining depth values and corresponding electric discharge machining current values required for machining the workpiece to a prescribed configuration and dimensions, the electric discharge machining current values in the series progressively changing with increasing machining depth value from a maximum permissible value consistent with the set electrode side surface undersize to a smaller value consistent with the set machining depth.