An electrochemical machining apparatus with a clamping device and an electrode aligned in the same direction includes a platen, a lower seat, an anode electrode and a cathode electrode. The platen and the lower seat are located relatively for clamping. A working space is formed between the platen and the lower seat for allowing a workpiece to be placed therein. The anode electrode is disposed on the platen and is electrically connected to the workpiece. The cathode electrode is disposed inside the lower seat and is corresponding to the working space. An isolation layer is disposed between the cathode electrode and the lower seat to avoid an electrical connection. A working gap with a constant distance is preserved between the cathode electrode and the workpiece for allowing an electrolyte to flow therethrough and performing electrochemical machining.