Disclosed are a line light source, a line printer head, and an image forming apparatus. The line light source includes a light waveguide unit which guides light emitted from a light emitting layer which is disposed between a bottom electrode and top electrodes, wherein the light waveguide unit is disposed on the top electrodes. Light is emitted through the surface area of light emitting areas defined by overlapping areas of the bottom electrode and the top electrodes. The light waveguide includes a plurality of openings, the sizes of which may be different than the surface area of the light emitting areas. The light emitting amount can be adjusted by adjusting the light emitting surface areas without reducing printing resolution of the image forming apparatus by employing the disclosed line light source as the line printer head.