An ink jet head circuit board is provided which has heaters to generate thermal energy for ink ejection as they are energized. This circuit board has the heaters formed with high precision to reduce their areas. It also has provisions to protect the electrode wires against corrosion and prevent a progress of corrosion. The substrate is deposited with the thin first electrodes made of a corrosion resistant metal. This is further deposited with the resistor layer. The second electrodes made of aluminum are deposited to overlap the first electrodes to form the heater without causing large dimensional variations among the heaters. With this construction, if a defect should occur in a protective layer on or near the heater, a progress of corrosion can effectively be prevented because the material of the resistor layer is more resistant to encroachment than aluminum and the first electrodes are corrosion resistant.