unit machined area 1a a sec cm 2 entered from the per unit area applied current amount operating device 19 and displaying device 26 for displaying on the display unit 17 the incoming machining expansion allowance dp u03bcm from the machining expansion allowance operating device 25 and the machining time tm sec entered from the machining time operating device 22 the optimum pulse current operating device 18 the per unit area applied current amount operating device 19 the overall applied current amount operating device 20 the total applied pulse number operating device 21 the machining time operating device 22 the memory 23 the machining stopping device 24 the machining expansion allowance operating device 25 and displaying device 26 cooperatively comprise the control unit 15 all other parts are identical to those shown in fig1 and will not be described in further detail operation of the electrochemical machining device will now be described with reference to the flowchart in fig7 prior to machining machining condition setting is started in the machining condition control section 15 of the control unit 12 at step s1 the machined area ar of the workpiece 1 is defined during step s2 while the machining gap gp is set according to the relationships shown by the curve gp in fig4 which is described in greater detail below at step s3 the premachining surface roughness rmo and target surface roughness rm 1 are set from the input device 16 by an operator at step s4 during step.