An incandescent bulb filament having a flat Light-emitting surface and high Lamp efficiency and an incandescent bulb using this filament are provided. This incandescent bulb filament is characterized in that it is a filament of ribbon shape placed on one plane, and it includes: spaced portions which are placed side by side with spaces; and connecting portions which connect the spaced portions electrically in series. Each spaced portion has a thickness that is one half the width of the spaced portion or more, and the space between at least one pair of adjacent spaced portions is less than five times the width of the spaced portion.