An ink jet head circuit board is provided which has heaters to generate thermal energy for ejecting ink as they are energized. This circuit board is so constructed as to reduce wire resistances for the heaters while at the same time preventing an increase in the size of the board and realizing a high-density integration of the heaters required for high resolution printing. This construction is made possible by forming electrode wires of first and second electrode wire layers to reduce an area that the wire patterns for the heater occupy on the circuit board. In reducing the effective thickness of protective insulation layer formed on the heater to prevent a possible degradation of thermal efficiency, one of the protective insulation layers over the electrode wires is removed from the heater, depending on the thickness of the electrode wires.