The invention relates to a surface light source device, which is characterized in that a light guide column is additionally arranged between a light emitting source and a light guide film so as to collect light emitted by the light emitting source and transmits the light to a light incoming surface of the light guide film, and the light guide film can be enabled to be small in thickness through a thickness gradually reducing structure design for the light guide column, so that a purpose of reducing the thickness of a traditional light guide plate can be achieved. Furthermore, the surface light source device can be applied to a side entering type backlight module and a display device, and can also be applied to the field of lighting.