A method and a device for electrochemically machining workpiece having blade end plates at the longitudinal both ends of a blade-shaped portion having aerofoil shape in cross section by extending and retracting divided electrodes. A part of the blade-shaped portion and one blade end plate continued therewith are electrochemically machined by advancing the main electrode in an acute angle direction relative to the longitudinal direction of the blade-shaped portion. At the same time or subsequently, the remaining part of the blade-shaped portion and the other blade end plate continued therewith are electrochemically machined by slidably advancing an auxiliary electrode along the slope of the main electrode forming an acute angle relative to the blade-shaped-portion-machining-surface. Thus, the number of the parts of an electrode unit can be reduced and the structure thereof can be simplified.